Biology

I. Introduction
Eukaryotes are characterized for their elaborate system of membranous organelles having its own unique array of glycoproteins and glycolipids and perform a particular set of functions. Because of cellular compartmentalization, functions are accomplished autonomously or in coordination. One key cellular function is vesicular transport responsible for carrying materials between specific compartments of organelles and mediated by SNAREs or soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein (SNAP) receptors. Kienle, Kloepper and Fasshaeur (2009) found more than 20 different SNARE proteins in model organisms. In Arabidopsis thaliana, there are 62 44 in Homo sapiens 30 in Caenorhabditis elegans 26 in Drosophila melanogaster and 24 in Saccharomyces cerevisiae. Basing on the above, SNAREs have undergone modification, duplication, and then diversification. This paper is aimed to discuss in full detail its structure, types, functions, contributions to modern biology, and related issues in medicine and scientific research, mechanism of action, and similarities and differences in human and plant SNARES. Personal critique on the methodologies and gaps on SNARE research will also be taken into consideration.

II. Structure
All SNAREs have a SNARE domain, a heptad repeat of 60 amino acids which is largely unstructured. During assembly, SNARE domains roll into a SNARE complex which reversibly dissociates under ATPase NSF and  INCLUDEPICTURE  httpwww.nature.com__charsalphablackmedbaseglyph.gif  MERGEFORMATINET -SNAP. The SNARE domains also serve as an earmark in the classification of SNAREs into Qa (syntaxins), Qb (SNAP-25 N-terminal CCD), Qc (SNAP-25 C-terminal CCD), and R-SNAREs. In the Q-SNARE, the central amino acid residue is glutamine while arginine in the R-SNARE. These amino acid residues form the zero ionic layer in the assembled SNARE core complex. When the zero ionic layer is exposed to water by breaking the flanking leucine zipper which destabilizes the SNARE complex and is the putative mechanism by which -SNAP and HYPERLINK httpen.wikipedia.orgwikiN-ethylmaleimide_sensitive_fusion_protein o N-ethylmaleimide sensitive fusion proteinNSF recycle the SNARE complexes after the completion of HYPERLINK httpen.wikipedia.orgwikiSynaptic_vesicle o Synaptic vesiclesynaptic vesicle HYPERLINK httpen.wikipedia.orgwikiExocytosis o Exocytosisexocytosis. Each of these groups form part of the SNARE complex, which in combination with cognate SNAREs generate functional SNARE complexes crucial in specific membrane fusions (Bock et al., 2001 Antonin et al., 2002 Kloepper et al., 2007 as cited in Ebine et al., 2008).

Bennett, Calakos, and Scheller (as cited in Teng, Wang,  Tang, 2001) were the first workers to clone syntaxin, which consists of two 35 kDa proteins currently known to be syntaxin 1A and 1B. Amino acid sequence analysis showed these proteins were 84 identical. It was first hypothesized that syntaxin is only localized in neuronal cells until it was later proven there were also non-neuronal homologs. In mammals, there were 15 syntaxins while seven in yeast (Teng, Wang,  Tang, 2001). Its primary structure has been identified successfully which will be explained in the succeeding sentences. Ibaraki et al. (1995) found structural differences in Syntaxin 3 from the mouse brain cDNA. They jointly discovered that at the carboxyl terminal, amino acid sequences of Syntaxin 3B and Syntaxin 3A varied. Syntaxin 3C contained 18 amino acids instead of 34 in syntaxins 3A and 3B. In addition, Syntaxin 3D has only 86 amino acids and did not possess putative transmembrane segments. Ravichandran and Roche (1997) deduced that the 301 amino-acid sequence of human syntaxin 5 shares 96 identity with rat syntaxin 5. Another important discovery about syntaxin is provided by Misura, Scheller, and Weis (2000). As cited in Brunger et al. (2009), syntaxin in the neuronal-Sec1-syntaxin 1a complex switches between closed and open conformations. Other SNAREs were prevented from interacting with the N-terminal domain of syntaxin in a closed conformation while in an open conformation, synataxins SNARE core domain can freely interact with synaptobrevin and SNAP-25. Margittai et al. (2003) as cited in Brunger et al. (2009) observed frequent switching between conformations with a 0.8 ms relaxation time. However, Chen et al. (2008) as cited in Brunger et al. (2009) only noted the closed conformation using NMR.

SNAP25 (synaptosome-associated protein 25kDa) contains a palmitoylated stretch of cysteine residues following the N-terminal of the Qb-SNARE domain which functions to increase membrane-interactions of these proteins (Gonzalo et al., 1999 as cited in Sanderfoot, 2007). The central portion of the protein is hinged tightly to the presynaptic membrane which permits free interaction with its other complex counterparts.  An additional function suggested by Rettig et al. (1996), Wiser et al. (1996), and Yokoyama et al. (as cited in Georgiev, 2002) is its regulation of calcium channels. The role of calcium in SNARE-mediated fusion will be explained later on in this paper.  

Meanwhile, the R-SNAREs are classified into two classes, longins and brevins. The former  contains a longin domain which is an N-terminal profilin-like fold containing 120-140 amino acid residues while the latter lacks this structure (Filippini et al., 2001 Gonzalez et al., 2001 Rossi et al., 2004 as cited in Ebine et al., 2008).  An important R-SNARE is SynaptobrevinVAMP (vesicle associated membrane protein) which binds to the t-SNAREs in vitro at their carboxyl terminals (Chapman et al., 1994 Hayashi et al., 1995 Kee et al., 1995 as cited in Georgiev, 2002).

A better understanding on the structure of the SNARE core complex would be achieved by reviewing the studies of Xiao et al. (2001), Antonin et al. (2002), and Strop et al. (2008). Before presenting their  results, it is noteworthy that as early as 1998, Fasshauer et al. (cited in Antonin et al., 2002) hypothesized that SNARE complexes are formed by four helices, arranged in a parallel fashion with the N termini at one end of the bundle and the C termini at the membrane-anchor end and connected by hydrophobic layers of interaction. Using the spin labeling electron paramagnetic resonance, Xiao et al. (2001) showed that the structural description of the neuronal SNARE complex reinforced Fasshauer et al. Evidence showed two identical syntaxin 1A components and N-terminal and C-terminal domains of SNAP-25 arranged in a parallel, four helix bundle. Antonin et al. (2002) identified that the four SNAREs in the endosomal core complex were Syntaxin 7, Syntaxin 8, Vti1b and EndobrevinVAMP-8. It was seen that Endobrevin is the a-helix Syntaxin 7, b-helix Vti1b, c-helix and Syntaxin 8, d-helix.  This bundle of helices is held together by both polar and ionic surface interactions. For instance Glu 179 in Syntaxin 7 forms a salt bridge with Arg 148 in Vti1b. Even in S. cerevisiae overall structure of the plasma membrane SNARE complex is very similar to both neuronal and endosomal types although sequence identity is relatively low (Strop et al., 2008). According to Sutton et al. (1998), radius of the four-helix bundle changes significantly over the length of the bundle. The variation in the radius is correlated with side chain packing in the core of the complex the layers with the largest side chain-packing volume show the largest radius.

III. Types
Originally, classification of SNAREs was based on the membrane component where they were required- either in the vesicles (v-SNAREs) or target compartments (t-SNAREs). The interaction between v- and t-SNARES is thought to bring the membranes close enough together so they can fuse. It was Jenas research team (as cited in Leabu, 2006) who discovered using atomic force microscopy and bilayer electrophysiological assays that full length t-SNARE and v-SNARE in opposing bilayers interact in a circular array forming ring-like channels to form conducting channels in the presence of calcium. Conversely, when v- and t-SNAREs are placed in solution, or when one of the SNAREs is in this condition, t-v-SNARE interactions did not form conducting channels. Therefore, t-SNAREs and v-SNAREs should be located in opposing membranes so that appropriate t-v-SNARE interactions would be formed. This leads to membrane fusion in the presence of calcium. Further analysis of SNARE reconstituted liposomes and bilayers showed that both SNAREs and Ca2 operate as the minimal fusion machinery. The results demonstrated a low fusion rate (16 min) between t- and v-SNARE-reconstituted liposomes in the absence of Ca2 while a vesicle fusion time of approximately 10s when t-v-SNARE liposomes were exposed to Ca2. An example is the mammalian synaptic complex where the v-SNARE of the synaptic vesicle is R-synaptobrevinVAMP-2 interacting with the pre-synaptic t-SNARE complex of Qa-Syntaxin and QbQc-SNAP25 (Hong, 2005 as cited in Sanderfoot, 2007).

Georgiev (2002) mentioned that present in mammals are these biologically important v-SNARES which include VAMP1synaptobrevin I, VAMP2synaptobrevin II, VAMP3cellubrevin, VAMP5, VAMP7T1-VAMP, VAMP8endobrevin, and synaptotagmin I, II, III, V, X. In addition mammalian t-SNARES consist of Syntaxin IA and IB, Syntaxin 2, Syntaxin 3, Syntaxin 4, SNAP25 A and B, and SNAP23Syndet.

Since the hydrophilic center of the SNARE core complex containing three and one glutamine and arginine, respectively was almost conserved, the QabcR rule was introduced. Details on this regard were previously elaborated.

However, Kloepper, Kienle, and Fasshauer (2007) refined the four major SNARE groups into 20 distinct subgroups. This elaborate classification was based on the analysis of SNARE sequences from 145 different species. There are five Qa-SNARE subgroups representing the target organelle to the major compartments which were numbered on the basis of its arrangement in the secretory pathway. For endoplasmic reticulum, it is coded I Golgi apparatus, II trans-Golgi network, IIIa digestive endosomes, IIIb and plasma membrane, IV. The SNARE intended for retrograde transport from Golgi to ER is designated as group I. Examples in this group are Syx18Ufe1 (QaI), Sec20 (QbI), Use1 (QcI), and Sec22 (RI). Only one SNARE, the Syn5Sed5, is involved in the ER to Golgi complex transport and within the Golgi. Known to be interacting partners, QbII and QcII, contain two factors and only one transport step is participated by each of these factors. The interaction partners of SNAREs located in the trans-Golgi network, the Syx16Tlg2, remain undetermined. However a possibility that Syx16Tlg2 might be in association with SNAREs in both adjacent Golgi apparatus and endosomal compartment is very plausible.  

IV. Functions
Primarily, SNARE proteins mediate vesicular trafficking via secretory and endocytic pathways in eukaryotic systems and form tight SNARE complexes through their SNARE domains. Hepp and Langley (2001) emphasized that vesicular trafficking is an essential event which requires membrane fusion as in fertilization, cell division, maintenance of subcellular compartments, protein and hormone secretion, and neurotransmitter release. In this section, functions of specific groups of SNARE proteins from different organisms will be illustrated.

In Drosophila melanogaster, syntaxin-1A homologue (syx) had roles other than neurotransmission. Schulze and Bellen (1996) found it is necessary for oogenesis and membrane biogenesis in nurse cells and cuticle deposition and neurotransmitter release in late embryogenesis. Mutation in syx genes resulted in rough eyes and wing notch which are indicative of cell death.

SNAP 25 functions in association with syntaxin and synaptobrevin causing the docking and fusion of vesicles with plasma membrane, resulting in hormone release (Gerst, 1999 as cited in Quintanar et al., 2003). In addition, the research of Masumoto et al. (1997) and Aguado et al. 1997) as cited in Quintanar et al. (2003) showed that SNAP 25 plays a crucial role in the release of PRL and ACTH in the GH4C1 and AtT-20 pituitary cell lines. It was also discovered that the C-terminus of SNAP 25 affects exocytosis. When 49 amino acids are deleted at the C terminus, exocytosis is reduced specifically in chromaffin cells (Wei et al., 2000 Criado et al., 1999 as cited by Fang et al., 2008) suggesting that N- to C-terminal zipping is the driving force of fusion events.

Kovacs-Nagy et al. (2009) investigated the functions of SNAP-25 at the genetic level. In their review, effects of SNAP-25 deficiency in the coloboma mutant and blind-drunk mouse models were presented. In the colonoma mutant mouse, there is a heterozygous deletion in chromosome 2 which contains the gene for SNAP-25 (Hess et al., 1992 as cited in Kovacs-Nagy et al., 2009). Consequently, this mutation leads to decrease in SNAP-25 expression and dopamine release by 50. This animal model is proposed for Attention Deficit Hyperactivity Disorder (ADHD) since the mouse exhibits locomotor hypersensitivity and learning deficiencies. Gene therapy using a functional SNAP-25 transgene lessened hyperactivity and restored dopaminergic neurotransmission (Wilson, 2000 as cited in Kovacs-Nagy et al., 2009).  In  2007, Jeans et al. (2007) as cited in Kovacz-Nagy et al. (2009) conducted the blind-drunk mouse experiment. It was identified that the phenotypes, ataxia and sensorimotor gating, were the results of a missense mutation leading to an isoleucine-threonine substitution in a conserved region of SNAP-25b. As a result, the mutant SNAP-25b increased its binding affinity to Syntaxin-1 twice compared to its wildtype. At the cellular level, exocytotic vesicle recycling was impaired. The previously mentioned phenotypes were characteristic of schizophrenia
In A. thaliana, the Qa-SNARE KNOLLESYP111 which is expressed in dividing cells of various developing tissues, controls vesicle fusion at the cell plate during cytokinesis according to Lukowitz et al. (1996) as cited in Ebine et al (2008). Also, when the plasma membrane-localized becomes impaired, A. thaliana becomes more susceptible to pathogens (Collins et al., 2003 as cited in Ebine et al. 2008), and mutation in SYP121 and its paralog SYP122 results in dwarfism and necrotic cell death (Assaad et al., 2004 as cited in Ebine et al., 2008). These experiments imply divergence of the SYP1 Qa-SNARE subfamily allowing it to perform various secretion-related functions in plants. There also seemed to be specialized functions in the Q-SNARES in both plant endocytic and vacuolar systems. Defective shoot gravitropic responses resulted when the Q-SNARE genes in A. thaliana (SYP22VAM3SGR3 and VTI11) mutated (Kato et al., 2002 Yano et al., 2003 as cited in Ebine et al., 2008).  There are more data suggesting that some plant SNAREs perform dual roles in development and physiological responses (Lipka, Kwon,  Panstruga, 2007).

V. Mechanism of action
According to Sanderfoot and Raikhel (2003), as the donor vesicle approaches the target membrane, the v-SNARE gain entry into the three-helix of the t-SNARE, forming the four-helix core SNARE complex that leads to vesicle fusion.  However, SNAREs cannot act alone because many factors should interplay to regulate vesicle fusion. These other factors are NSF,  INCLUDEPICTURE  httpwww.plantcell.orgmathagr.gif  MERGEFORMATINET -SNAP, a peripheral membrane protein from the Sec1p family and a small GTPase of theRabfamily (Malhotra et al. 1988Y. Satoet al. 1997 Eakle et al. 1988 as cited in Sanderfoot and Raikhel, 1999). These transport vesicles carry an activated v-SNAREanda GTP-boundform ofRab while in the target membrane bears a t-SNARE bound to an Sec1p homolog. Displacement of the Sec1p homolog by RabGTP causes a conformational change allowing the t-SNAREto freely interact with the v-SNARE. Then the v-andt-SNAREs zip up through their coiled domains, providing the energy sufficient to fuse lipid bilayers of the vesicle and the target. After which, the v-t-SNAREpair binds with the  INCLUDEPICTURE  httpwww.plantcell.orgmathagr.gif  MERGEFORMATINET -SNAP recruiting NSF to the SNAREcomplex. Because of the ATPase activity of NSF, it dissociates the SNARE core complex consequently releasing the v-SNAREfor recycling by the donor andpreparing the t-SNAREfor subsequent fusionevents (Sanderfoot and Raikhel, 1999).

SNARE-induced membrane fusion is said to be calcium-dependent. Physiology taught that though calcium is present in abundant amounts within cells, it is sequestered and would only be available by demand (Jeremic et al. 2006 as cited in Leabu, 2006). Exposure to certain cellular stimulus would trigger an increase in Ca2concentration in a cell within a short span of time. The research teams of Schneider, Cho, Jena, Jeremic, and Anderson revealed that calcium ion channels are directly associated with t-SNARE (SNAP-23) present at the base of porosomes, the site of vesicle docking and fusion. Because calcium in cells is in a hydrated state, Ca(H2O)n2 and measures 6 , it would not fit between the 2.83  space occupied by t-v-SNAREs between bilayers (Jeremic et al., 2004 Jeremic, Cho, and Jena, 2004 as cited in Leabu, 2006).

The experiment of Jeremic, Cho, and Jena (2004) as cited in Leabu (2006) proved that in the absence of calcium, t- and v-SNARE vesicles do not fuse while its presence causes vesicles to aggregate. Two years later, NSF-ATP was noted to disassemble SNARE core complex (Jeremic et al., 2006 as cited in Leabu, 2006) because it significantly inhibited aggregation aside from proteoliposome fusion. This disassembly of the SNARE core complex will render the bilayers widely separated, thereby membrane fusion is prevented. In the same way, when the restricted area between adjacent bilayers delineated by the t-v-SNARE complex is formed, then size of the hydrated Ca2ions would be too large to be sandwiched between the bilayers, thus, addition of Ca2would not exert any effect. However, when Ca2 is present during the interaction of t-SNARE and v-SNARE vesicles, calcium phosphate bridges are formed which expels water around the calcium ion ultimately leading to lipid mixing and membrane fusion. The calcium bridging of apposing bilayers releases water from the hydrated Ca2ion, destabilizing the bilayers and fusing the membranes. Moreover, binding of calcium to the phosphate heads of apposing bilayers also displaces loosely coordinated water at the phosphate groups, adding to the destabilization of the lipid layer (Jeremic, Cho, and Jena, 2004 as cited in Leabu, 2006). With regard to the number of SNARE core complex needed for membrane fusion, van den Bogaart et al. (2009) found that only one is sufficient.

VI. Contributions to Modern Biology
SNAREs have contributed to the many facets of modern biology. For more obvious reasons, it has helped advance cell and molecular biology, and other fields such as developmental, reproductive, and evolutionary biology.

At first, SNAREs were thought to be the core catalysts of cellular fusion. Later on, there were also other proteins that are as essential to the SNAREs in fusion events. Then, in 2006, researchers at two different institutions found that SNAREs alone could also cause cell membrane lysis. This finding brought substantial confusion to modern biology. Until then, the leading model was that these other proteins were involved in regulating SNARES and had no significant role in fusion. Wickner and his colleagues identified a key player in cell membrane fusion and there are the Rab and SM proteins which prevent membranes from leaking or rupturing during fusion. Suedhof of the University of Texas described SNAREs by themselves to be powerful but hapless because they need to be organized by these proteins. The SNARE hypothesis has formed the basis for specific docking and fusion of transport vesicles with their target membranes. This understanding helped cellular biologists provide explanation on many cellular processes such as Golgi cisternae stacking, retrograde transport, among others.

In human developmental biology, SNAREs have helped students better understand the acrosome reaction during fertilization. According to Ramalho-Santos et al. (2000), the acrosome of mammalian sperm contains a v-SNARE  (synaptobrevin), and t-SNARE (syntaxin 1) along calcium sensor synaptotagmin I. During the acrosome reaction, SNAREs present in the sperm are sloughed off and this parallels with the release of sperm membrane vesicles and acrosomal contents. It is also the SNAREs and other sperm components are responsible for asynchronous male DNA decondensation.
SNARES have also helped biologists unlock the mysteries of plant evolution. The presence of three major and several subgroups of plasma membrane syntaxins by Sanderfoot (2007) provide strong evidence that expansion of plant PM-syntaxins may be linked to multicellularity (Dacks and Doolittle, 2002 as cited in Sanderfoot, 2007). New evidence in their work pointed towards its linkage with radiation of land plants. A vertical inheritance of the housekeeping SYP13 group from the chlorophyte ancestors is highly plausible.  Then the mosses gave rise to the SYP12 group which has specialized roles of secretion, defense related or cell plate formation. Then, there is the evolution of a specialized syntaxin (SYP11KNOLLE) which exclusively operates in seed plant cytokinesis. Subsequent specializations (PEN1ROR2 and SYP124) would arise to further differentiate some additional functions.

VII. Related issues in Medicine and Scientific Research
In the medical field neuropathology, SNARE protein dysregulation was pinpointed to offer the genetic basis for schizophrenia based on a number of expression studies. This portion of the paper will enumerate these studies. In 1997, Honer et al. (1007) as cited in Johnson, Oliver, and Davies (2008) examined the cingulated cortex of 18 schizophrenic patients and 24 controls using ELISA, immunoblotting, and immunocytochemistry. They observed among the schizophrenics, elevated levels of syntaxin while no changes in SNAP-25 and synaptophysin.  Sokolov et al. (2000) in Johnson, Oliver, and Davies (2008) analyzed the left temporal gyrus or the Brodmanns area 22 and noticed an age-dependent decrease in syntaxin and SNAP-25 among schizophrenics. Quantitative PCR of mRNA levels was the method of analysis. Mukaetova-Ladinska et al. (2002) subjected the cerebellum of eight schizophrenic patients and controls to competitive ELISA and immunohistochemistry. Their findings showed selective loss of SNAP-25 in the schizophrenic tissue without changes in synaptophysin. There was an almost 50 reduction in SNAP-25 levels in schizophrenic patients as indicated by the Western blot of the whole hippocampus of seven schizophrenics, eight bipolars, and eight controls (Thompson et al., 2003 as cited in Johnson, Oliver, and Davies, 2008). The quantitative immunoblotting of the prefrontal cortex by Halim et al. (2003) reduced synaptobrevin by 22 yet there was no change in SNAP-25 (as cited in Johnson, Oliver,  Davies, 2008). Scarr et al. (2006) who used Western blot analysis and real-time polymerase chain reaction in the Brodamanns area 9 of dorsal prefrontal cortex noted that both SNAP-25 and synaptophysin increased in the bipolar samples but unchanged in the schizophrenics (as cited in Johnson, Oliver,  Davies, 2008).

VIII. Human and plant SNARE proteins
The SNARE system remained conservative from the yeast to the human genomes therefore, similarities would be expected. Green plants have SNAREs similar to humans that operate between ER and Golgi apparatus. Members of the Qa-SYP3 family in plants have been known to share homology with human syntaxin 5 (Rancour et al., 2004 Uemura et al., 2004 as cited in Bassham et al., 2008).  As in mammals, all angiosperms have proteins similar to Qa-SYP81, Qb-SEC20, Qc-USE1 and RSEC22. There were also plant SNAREs similar to human Golgi SNARE complex (Hong et al., 2005 as cited in Sanderfoot, 2007) which consist of Qa-SYP3, Qb-MEMB1, Qc-BET1 and RSEC22. When few of these genes were investigated, proteins in A. thaliana function similarly with the animal homologues (Chatre et al., 2005 as cited in Sanderfoot, 2007).

Later in the Golgi stacks, there is replacement of some SNAREs in the early-Golgi complex by other SNAREs as shown by Parlati et al. (2002) and Volchuk et al. (2004) as cited in Sanderfoot (2007). For instance, the mammalian Qb-Membrin is replaced by Qb-GS28 and Qc-mBet1 is replaced by Qc-GS15 (Volchuk et al., 2004 as cited in Sanderfoot, 2007). In addition, plants have Qb-GS28Gos1p homologues and Qc-SFT which is a BET1-like protein presumably operating in the later stacks of the Golgi (Bassham et al., 2008).

The Qc-SYP5 group (SYP51 and 52 in A. thaliana) has a human counterpart which is Syntaxin 8 (Sanderfoot et al., 2000 Sanderfoot, 2007 as cited in Bassham et al., 2008).

In green plants, SNAP33-type proteins have been demonstrated to have similar roles to the mammalian SNAP25. SNAP33-like were known to be associated with general secretion (Kargul et al., 2001 as cited in Bassham et al., 2008), pathogen defense (Collins et al., 2003 as cited in Bassham et al., 2008), and for cell plate formation during cytokinesis (Heese et al., 2001 as cited in Bassham et al., 2008). Compared to SNAP25, SNAP33 proteins have an N-terminal extension different from that in SNAP29, SNAP47 or Sec9p. They also lack the palmitoylation site of SNAP25-like proteins (Sanderfoot, 2007).

Human VAMP7 is phylogenetically more similar to the VAMP71 clade (VAMP711-to-714 in A. thaliana) which is found in all green plants. Members of this clade are localized in the organelles in the endosomal and vacuolar system (Uemura et al., 2004 Carter et al., 2004 as cited in Bassham et al., 2008), similar to the yeast and human VAMP7 SNAREs (Pryor et al., 2004 Wen et al., 2006 as cited in Basshman et al., 2008). The VAMP72 group (VAMP721-to-728 in Arabidopsis) is only characteristic of green plants (Sanderfoot, 2007 as cited in Bassham et al., 2008), and is involved in secretion.

IX. Critique
In this last part of the research paper, I focused my critique on why some SNARE proteins in plants perform dual functions in development and physiological responses. Is it because there were variations in expression pattern and location at the subcellular level, or presenceabsence of specific regulatory proteins, or changes in vesicular cargo

I also noted that the findings in the expression studies on schizophrenia could not be easily compared because the methodologies varied, the profile of the samples differed, and different brain regions were examined. Therefore it is necessary that future researchers should employ a combination of functional analysis, characterization of mice SNARE mutations, and more human genetic studies of the SNARE machinery would help give clarity on the molecular and cellular mechanisms of both neurodevelopmental and neurotransmitter abnormalities in schizophrenia.

While it was proven that abnormal SNARE proteins cause mental health illnesses, pharmaceutical companies could explore the possibility of incorporating these proteins into antipsychotic drugs and conduct clinical trials in the near future considering that families are greatly burdened by the effects of mental health illness.