Crystal structure of human T cell leukemia virus type 1 gp21 ectodomain crystallized as a maltose-binding protein chimera reveals structural evolution of retroviral transmembrane proteins

Abstract

Retroviral entry into cells depends on envelope glycoproteins, whereby receptor binding to the surfaceexposed subunit triggers membrane fusion by the transmembrane protein (TM) subunit. We determined the crystal structure at 2.5-Å resolution of the ectodomain of gp21, the TM from human T cell leukemia virus type 1. The gp21 fragment was crystallized as a maltose-binding protein chimera, and the maltose-binding protein domain was used to solve the initial phases by the method of molecular replacement. The structure of gp21 comprises an N-terminal trimeric coiled coil, an adjacent disulfide-bonded loop that stabilizes a chain reversal, and a C-terminal sequence structurally distinct from HIV type 1͞simian immunodeficiency virus gp41 that packs against the coil in an extended antiparallel fashion. Comparison of the gp21 structure with the structures of other retroviral TMs contrasts the conserved nature of the coiled coil-forming region and adjacent disulfide-bonded loop with the variable nature of the C-terminal ectodomain segment. The structure points to these features having evolved to enable the dual roles of retroviral TMs: conserved fusion function and an ability to anchor diverse surface-exposed subunit structures to the virion envelope and infected cell surface. The structure of gp21 implies that the N-terminal fusion peptide is in close proximity to the C-terminal transmembrane domain and likely represents a postfusion conformation.

An approach to crystallizing proteins by metal‐mediated synthetic symmetrization

“…The first approach is based on the observation that both T4L and MBP have been successfully used to crystallize otherwise difficult proteins, including membrane proteins and amyloid proteins. 10,[57][58][59][60][61] The mutation pairs characterized in this study could be readily used to increase the chance of getting crystals. The crystal packing arrangements of such fusion proteins would depend on surface properties of the target protein and would therefore likely be different from the structures presented here.…”

De Novo Design of Peptide Immunogens That Mimic the Coiled Coil Region of Human T-cell Leukemia Virus Type-1 Glycoprotein 21 Transmembrane Subunit for Induction of Native Protein Reactive Neutralizing Antibodies

“…The transmembrane and cytoplasmic tail regions are located at the C terminus. The recently solved crystal structure of the central segment of the HTLV-1 transmembrane subunit as a chimera with maltose-binding protein shows that the HTLV-1 TM does not deviate from the conserved spatial organization and general organization (31).…”

Artificial Ion Channel Biosensor in Human Immunodeficiency Virus gp41 Drug Sensing

“…It was shown to respond specifically to peptides and inhibitors known to bind in the hydrophobic pocket, with a resulting decrease in the current observed in the presence of redox probe Detection of low molecular weight inhibitors and C-peptides which bind to the N-terminal coiled coil of several Class 1 viral fusion domains has been shown to be an effective strategy for identifying viral fusion inhibitors 6 . In many class 1 viruses, the C-peptide is ill-defined in the post-fusion conformation, either due to extended strand structure for the C-terminal domain 43,44 or an unknown three-dimensional structure. On the other hand, the coiled coil domain is usually recognizable from sequence analysis 45,46 .…”