Kwong, P.D., Wyatt, R., Robinson, J., Sweet, R.W., Sodroski, J., Hendrickson, W.A. (1998)

Structure of an HIV gp120 envelope glycoprotein in complex with the CD4

receptor and a neutralizing human antibody. Nature 393:648-659.

Nicki Harmon, Samantha Hurndon, & Zeb RussoBioinformatics Lab 10/19/2011

Outline

• HIV causes the destruction of CD4 lymphocytes

HIV causes destruction of CD4 lymphocytes

• Entry of HIV virus into host cells is mediated by viral envelope glycoproteins

• These glycoproteins are arranged in oligomeric, most likely trimeric spikes along the surface of the virion

• The surface of the spike is primarily gp120• gp120 contains five variable regions (V1-V5)• both conserved and variable gp120 regions are heavily glycosylated• this glycosylation probably modulates the immunogenicity and

antigenicity of gp120• gp120 is the main target for antibodies• gp120 will bind to glycoprotein on CD4 and acts as main receptor• gp120 binds to the most amino-terminal of the four immunoglobulin like

domains of CD4

GP120 is a primary binding region for HIV

• mutagenesis has found critical regions in both gp120 and CD4 for binding• CD4 binding induces a conformation change in gp120 which

exposes/forms a chemokine receptor• This chemokine receptor for CCR5 and CXCR4 serve as obligate secondary

receptors for HIV entry into the cell• There are other more conserved regions of gp120 that seem to be

involved in chemokine-receptor binding• CD4i (CD4 induced) antibodies block the binding of the gp120-CD4

complex to the chemokine receptor• HIV and related retroviruses belong to a class of enveloped fusogenic

viruses, all which require post-translational cleavage for activation.• since gp120 is so important in receptor binding and in interactions with

antibodies, info about it is important

Crystal structure at 2.5 Å of a HIV gp120 core with associated proteins

• Gp120 in red, CD4 in yellow, CD4i antibody 17b in dark and light blue

• Due to the fact that gp120 is extensively glycosylated and shows great conformational heterogeneity, radical modification of the protein surface was devised to image it.

Secondary Structure in GP120• core is made up of 25 β-sheets, 5 α-helices, and

10 defined loop segments• the polypeptide chain is folded into two main

domains along with some digressions from this body

• Inner domain contains a two-helix, two-sheet bundle with a small five sheet β-sandwich at its termini-proximal end and a projection from the distal side where the V1/V2 stem originates.

• Outer domain is a stacked double barrel that lies alongside inner domain so that the both barrel axes are roughly parallel to each other.

• There is a ‘minidomain’ which is comprised of four antiparallel β-sheets that create a ‘bridging sheet’ that is in contact with both the inner and outer domains

• structure based alignment shows conservation despite the variability in HIV strains

Great similarities between HIV-1,HIV-2, and SIV

• α-Carbon trace shows the conservation of disulfide bridges

• Sequence alignment shows similarity between HIV strains and SIV as well a s solvent accessability

CD4 is bound to gp120 in a depression formed by the interface of the inner and

outer domains

• Electron density in the Phe43 binding site• Electrostatic potential across the surfaces

of gp120 and CD4

More binding of CD4 and gp120

• 3d shows contact surfaces• 3e shows mutational

hotspots on both CD4 and gp120

• 3f elucidates side vs main-chain contributions to gp120 surface

• 3g demonstrates gp120 sequence variability

• 3h shows the Phe43 cavity

A closer look at the Phe43 cavity

Antibody interactions with gp120• Interactions between gp120 and CD4i

antibody, highlighting the V3 region

Overview of gp120 activity during HIV fusion to lymphocytes