Zrusso Biol 368 week 7
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Journal Club Prep
- My partners are Samantha Hurndon and Nicki Harmon and we are working on the Kwong paper.
Biological Terms
- Oligomeric - a polymer molecule consisting of a small number of monomers. Retrieved from [1] on 10/12/11
- Chemokine - any of a group of chemotactic cytokines that are produced by various cells (as at sites of inflammation), that are thought to provide directional cues for the movement of white blood cells (as T cells, monocytes, and neutrophils), and that include some playing a role in HIV infection because the cell surface receptors to which they bind are also used by specific strains of HIV for entry into cells. Retrieved from [2] on 10/12/11
- Fusogenic - Facilitating fusion, especially relating to cells. Retrieved from [3] on 10/12/11
- Prophylactic - defending or protecting from disease or infection, as a drug. Retrieved from [4] on 10/12/11
- Ternary - consisting of three different elements or groups. Retrieved from [5] on 10/12/11
- Prolate - elongated along the polar diameter, as a spheroid generated by the revolution of an ellipse about its longer axis ( opposed to oblate). Retrieved from [6] on 10/12/11
- Interfacial - included between two faces. Retrieved from [7] on 10/12/11
- Antigenic - having the properties of any substance that can stimulate the production of antibodies and combine specifically with them. Retrieved from [8] on 10/12/11
- Proteolytic - the breaking down of proteins into simpler compounds, as in digestion. Retrieved from [9] on 10/12/11
- Glycocalyx - a polysaccharide or glycoprotein covering on a cell surface. Retrieved from [10] on 10/12/11
Paper Outline
- Introduction
- HIV-1, HIV-2 and their cousin the Simian immunodeficiency viruses (SIV) destroy CD4 lymphocytes in their hosts, which results in AIDS
- 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
- These spikes are anchored to the viral membrane by gp41 transmembrane protein
- 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
- 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
- V3 is the principle determinant of chemokine receptor specificity
- 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.
- Some share protein sequence similarity while others are quite distinctive.
- since gp120 is so important in receptor binding and in interactions with antibodies, info about it is important
- In this paper is reported the crystal structure at 2.5 Å detail a partially deglycosylated HIV-1 gp120 core bound to a two domain fragment of CD4 receptor and to an antigen binding fragment (Fab) 17b, which acts on a CD4i epitope.
- Structure Determination
- 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.
- truncations were made at the termini and at variable loops in various combinations from various strains. These variants were then heavily deglycosylated and produced complexes with
- This was done because a theoretical analysis showed an increase in probable crystal formation with the reduction of surface heterogeneity and trials with multiple variants.
- After many combinations, crystals were obtained of a ternary complex that contained a truncated gp120, the N-terminal of two domains of CD4, and a Fab from 17b.
- the gp120 crystallized was from HIV-1 strain HXBc2
- deletions of 52 residues from N-terminus and 19 from C-terminus.
- Gly-Ala-Gly tripeptide substitutions for 67 V1/V2 loop residues and 32 V3 loop residues
- removal of all sugar groups beyond the linkages between the two core N-acetyl-glucosamine residues.
- removal of 90% of total carbohydrate but retains 80% of non-variable loop protein
- capacity to interact with CD4 and relevant antibodies is preserved at or near wild-type levels.
- 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.
