Novel Fold and Carbohydrate Specificity of the Potent Anti-HIV Cyanobacterial Lectin from Oscillatoria agardhii

Leonardus M.I. Koharudin,Angela M. Gronenborn,William Furey

doi:10.1074/jbc.m110.173278

Abstract

Oscillatoria agardhii agglutinin (OAA) is a recently discovered cyanobacterial lectin that exhibits potent anti-HIV activity. Up to now, only its primary structure and carbohydrate binding data have been available. To elucidate the structural basis for the antiviral mechanism of OAA, we determined the structure of this lectin by x-ray crystallography at 1.2 Å resolution and mapped the specific carbohydrate recognition sites of OAA by NMR spectroscopy. The overall architecture of OAA comprises 10 β-strands that fold into a single, compact, β-barrel-like domain, creating a unique topology compared with all known protein structures in the Protein Data Bank. OAA sugar binding was tested against Man-9 and various disaccharide components of Man-9. Two symmetric carbohydrate-binding sites were located on the protein, and a preference for Manα(1-6)Man-linked sugars was found. Altogether, our structural results explain the antiviral activity OAA and add to the growing body of knowledge about antiviral lectins.

Highlights

HIV infection occurs via virus-cell and cell-cell fusion mediated by the two viral envelope glycoproteins gp120 and gp41 (1–3). gp120 interacts with the CD4 receptor of the host cell, resulting in a conformational change in gp120 that eventually leads to the insertion of the fusion peptide of gp41 into the target membrane, causing membrane fusion (4)
The protein starts at Ala-2, with Met-1 being completely removed by the E. coli N-terminal methionine aminopeptidase during protein expression, we kept the numbering according to Sato and Hori (20) for consistency
In contrast to previous suggestions that implied a similar structure to bacterial lectins or to those of cyanobacteria or marine algae, such as Eucheuma serra agglutinin 2 (ESA-2) and Myxobacterium hemagglutinin (MBHA) (19), the three-dimensional structure of Oscillatoria agardhii agglutinin (OAA) is clearly distinct from any known lectins

Summary

Introduction

HIV infection occurs via virus-cell and cell-cell fusion mediated by the two viral envelope glycoproteins gp120 and gp41 (1–3). gp120 interacts with the CD4 receptor of the host cell, resulting in a conformational change in gp120 that eventually leads to the insertion of the fusion peptide of gp41 into the target membrane, causing membrane fusion (4). No crystal structures for protein-carbohydrate complexes are available for scytovirin and actinohivin, sugar binding studies revealed specificities for Man␣(1–2)Man␣(1– 6)Man␣(1– 6)Man (17) and Man␣(1–2)Man (18), respectively.

Results

Conclusion