Peripherin-2: an intracellular analogy to viral fusion proteins.

The C-terminus of the intracellular retinal rod outer segment disk protein peripherin-2 binds to membranes, adopts a helical conformation, and promotes membrane fusion, which suggests an analogy to the structure and function of viral envelope fusion proteins. Nuclear magnetic resonance (NMR) data and fluorescence data show that a 63-residue polypeptide comprising the C-terminus of bovine peripherin-2 (R284-G346) binds to the membrane mimetic, dodecylphosphocholine micelles. High-resolution NMR studies reveal that although this C-terminal fragment is unstructured in solution, the same fragment adopts helical structure when bound to the micelles. The C-terminus may be a member of the class of intrinsically unstructured protein domains. Using methods developed for the G-protein coupled receptor rhodopsin, a model for the structure of the transmembrane domain of peripherin-2 was constructed. Previously published data showed that both peripherin-2 and viral fusion proteins are transmembrane proteins that promote membrane fusion and have a fusion peptide sequence within the protein that independently promotes membrane fusion. Furthermore, the fusion-active sequence of peripherin-2 exhibits a sequence motif that matches the viral fusion peptide of influenza hemagglutinin (HA). These observations collectively suggest that the mechanism of intracellular membrane fusion induced by peripherin-2 and the mechanism of enveloped viral fusion may have features in common.