Solid-state NMR spectroscopy of the HIV gp41 membrane fusion protein supports intermolecular antiparallel ? sheet fusion peptide structure in the final six-helix bundle state

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Solid-state NMR spectroscopy of the HIV gp41 membrane fusion protein supports intermolecular antiparallel ? sheet fusion peptide structure in the final six-helix bundle state

Publication date: Available online 16 November 2013
Source:Journal of Molecular Biology

Author(s): Kelly Sackett , Matthew J. Nethercott , Zhaoxiong Zheng , David P. Weliky

The HIV gp41 protein catalyzes fusion between viral and target cell membranes. Although the ~20-residue N-terminal fusion peptide (FP) region is critical for fusion, the structure of this region is not well-characterized in large gp41 constructs that model the gp41 state at different times during fusion. This paper describes solid-state NMR (SSNMR) studies of FP structure in a membrane-associated construct (FP-Hairpin) which likely models the final fusion state thought to be thermostable trimers with six-helix bundle structure in the region C-terminal of the FP. The SSNMR data show that there are populations of FP-Hairpin with either ? helical or ? sheet FP conformation. For the ? sheet population, measurements of intermolecular 13C-13C proximities in the FP are consistent with a significant fraction of intermolecular antiparallel ? sheet FP structure with adjacent strand crossing near L7 and F8. There appears to be negligible in-register parallel structure. These findings support assembly of membrane-associated gp41 trimers through inter-leaving of N-terminal FPs from different trimers. Similar SSNMR data are obtained for FP-Hairpin and a construct containing the 70N-terminal residues of gp41 (N70) which is a model for part of the putative pre-hairpin intermediate state of gp41. FP assembly may therefore occur at an early fusion stage. On a more fundamental level, similar SSNMR data are obtained for FP-Hairpin and a construct containing the 34N-terminal gp41 residues (FP34) and support the hypothesis that the FP is an autonomous folding domain.
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