SNARE protein

Overview

Diagram of the exocytosis machinery involving SNARE proteins.

SNARE proteins, or Soluble NSF Attachment Protein Receptors, are a large protein superfamily consisting of more than 60 members in yeast and mammalian cells. They are essential for the process of vesicle fusion, which is a critical step in the transport of molecules within cells. SNARE proteins mediate the fusion of vesicles with their target membranes, a process that is vital for the release of neurotransmitters in neurons, hormone secretion, and other cellular processes.

Structure and Function

Illustration of the zero layer in the SNARE complex.

SNARE proteins are characterized by the presence of a SNARE motif, which is a stretch of 60-70 amino acids that form coiled-coil structures. These proteins are divided into two categories: v-SNAREs (vesicle SNAREs) and t-SNAREs (target SNAREs). The interaction between v-SNAREs and t-SNAREs forms a SNARE complex, which brings the vesicle and target membranes into close proximity, facilitating membrane fusion.

The SNARE complex is a four-helix bundle, with each helix contributed by one of the SNARE proteins. The core of this complex is known as the "zero layer," which is composed of highly conserved residues that are crucial for the stability and function of the complex.

Mechanism of Action

Formation of the trans-SNARE complex with Munc18 SM protein.

The process of vesicle fusion begins with the formation of a trans-SNARE complex, where v-SNAREs on the vesicle membrane interact with t-SNAREs on the target membrane. This interaction is facilitated by SM proteins, such as Munc18, which stabilize the SNARE complex and regulate its assembly.

Once the trans-SNARE complex is formed, it undergoes a conformational change that brings the membranes into close proximity, leading to the formation of a fusion pore. This pore expands, allowing the contents of the vesicle to be released into the target compartment.

Regulation and Modulation

Opening of a fusion pore during exocytosis.

The activity of SNARE proteins is tightly regulated by various factors, including post-translational modifications such as palmitoylation. Palmitoylation of SNARE proteins can affect their localization and function, thereby modulating vesicle fusion events.

Diagram showing the palmitoylation of a protein.

Additionally, SNARE proteins are targets for various toxins, such as botulinum toxin and tetanus toxin, which cleave SNARE proteins and inhibit neurotransmitter release, leading to paralysis.

Clinical Significance

Presynaptic targets of clostridial neurotoxins.

SNARE proteins play a crucial role in the nervous system, and their dysfunction is associated with several neurological disorders. For example, mutations in SNARE proteins have been linked to conditions such as epilepsy, schizophrenia, and autism spectrum disorders.

Structure of tetanus neurotoxin, which targets SNARE proteins.

Understanding the mechanisms of SNARE-mediated vesicle fusion and its regulation is essential for developing therapeutic strategies for these disorders.

Related Pages

• Vesicle fusion
• Neurotransmitter release
• Botulinum toxin
• Tetanus toxin