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Trimeric HIV Env provides epitope occlusion mediated by hypervariable loops.

Moscoso CG, Xing L, Hui J, Hu J, Kalkhoran MB, Yenigun OM, Sun Y, Paavolainen L, Martin L, Vahlne A, Zambonelli C, Barnett SW, Srivastava IK, Cheng RH - Sci Rep (2014)

Bottom Line: A prominent basal quaternary location of V2 and V3' that challenges previous reports would facilitate gp41-independent gp120-gp120 interactions and suggests a quaternary mechanism of epitope occlusion facilitated by hypervariable loops.Deletion of V2 resulted in dramatic exposure of basal, membrane-proximal gp41 epitopes, consistent with its predicted basal location.The structural features of HIV-1 Env characterized here provide grounds for a paradigm shift in loop exposure and epitope occlusion, while providing substantive rationale for epitope display required for elicitation of broadly neutralizing antibodies, as well as substantiating previous pertinent literature disregarded in recent reports.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cellular Biology, University of California, Davis, CA 95616.

ABSTRACT
Hypervariable loops of HIV-1 Env protein gp120 are speculated to play roles in the conformational transition of Env to the receptor binding-induced metastable state. Structural analysis of full-length Env-based immunogens, containing the entire V2 loop, displayed tighter association between gp120 subunits, resulting in a smaller trimeric diameter than constructs lacking V2. A prominent basal quaternary location of V2 and V3' that challenges previous reports would facilitate gp41-independent gp120-gp120 interactions and suggests a quaternary mechanism of epitope occlusion facilitated by hypervariable loops. Deletion of V2 resulted in dramatic exposure of basal, membrane-proximal gp41 epitopes, consistent with its predicted basal location. The structural features of HIV-1 Env characterized here provide grounds for a paradigm shift in loop exposure and epitope occlusion, while providing substantive rationale for epitope display required for elicitation of broadly neutralizing antibodies, as well as substantiating previous pertinent literature disregarded in recent reports.

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Related in: MedlinePlus

Schematic representation of gp140 demonstrates intersubunit associations, relaxation of trimeric diameter upon deletion of V2.(A) The gp140 trimer was compared with the gp140ΔV2, gp140-CD4m and gp140ΔV2-CD4m maps. The degree of gp120-gp41 interface strength appears to decrease as a function of both V2 deletion and CD4m conjugation, with the gp140ΔV2-CD4m map representing the most “open” state. Inclusion of the V2 loop also results in a smaller trimeric diameter (100 Å), though the diameter remains unchanged in the gp140ΔV2, gp140-CD4m and gp140ΔV2-CD4m maps (110 Å). (B) 2D comparison of gp140ΔV2TV1 with full length constructs gp140TV1, gp140DU156.1, gp140CAP239 and gp140CAP45 reveals that full length constructs all had smaller trimeric diameters (99–103 Å) than gp140ΔV2TV1 (110 Å), indicative of closer intersubunit associations in full-length constructs than in ΔV2 constructs. Scale bar = 75 Å.
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f4: Schematic representation of gp140 demonstrates intersubunit associations, relaxation of trimeric diameter upon deletion of V2.(A) The gp140 trimer was compared with the gp140ΔV2, gp140-CD4m and gp140ΔV2-CD4m maps. The degree of gp120-gp41 interface strength appears to decrease as a function of both V2 deletion and CD4m conjugation, with the gp140ΔV2-CD4m map representing the most “open” state. Inclusion of the V2 loop also results in a smaller trimeric diameter (100 Å), though the diameter remains unchanged in the gp140ΔV2, gp140-CD4m and gp140ΔV2-CD4m maps (110 Å). (B) 2D comparison of gp140ΔV2TV1 with full length constructs gp140TV1, gp140DU156.1, gp140CAP239 and gp140CAP45 reveals that full length constructs all had smaller trimeric diameters (99–103 Å) than gp140ΔV2TV1 (110 Å), indicative of closer intersubunit associations in full-length constructs than in ΔV2 constructs. Scale bar = 75 Å.

Mentions: The gp140 and gp140ΔV2 maps, with and without CD4m, were determined to have a gradient of gp120-gp41 interface “open” states, as determined by the extent of intensity at the interface region. The unliganded gp140 map had the strongest interface between gp120 and gp41 observed of all four maps, followed by the gp140ΔV2 map, then the gp140-CD4m and lastly the gp140ΔV2-CD4m map (Fig. 4A). As such, it appears that both the V2 loop and CD4m binding contribute to the degree of “open” state, putatively exposing novel epitopes at the gp120-gp41 interface region. Given the propensity of V2 to promote interprotomeric gp120-gp120 contacts via the QNE, we also observed a smaller trimeric diameter when comparing the gp140 and the gp140ΔV2 maps. The trimeric diameter remained unchanged between the gp140ΔV2, gp140-CD4m and gp140ΔV2-CD4m maps, resulting from the outward density shift promulgated by CD4m binding (Fig. 4A). Likewise, we observed that the smaller trimeric diameter is apparent in other clade C trimers, namely from the CAP45.2.00.G3, CAP239.2.00.G3J and Du156.1 strains (Fig. 4B). Measurements of trimeric diameter of ΔV2 compared to full-length strains revealed that the full length strains had smaller trimer diameters (99 to 103 Å) compared to ΔV2 (110 Å).


Trimeric HIV Env provides epitope occlusion mediated by hypervariable loops.

Moscoso CG, Xing L, Hui J, Hu J, Kalkhoran MB, Yenigun OM, Sun Y, Paavolainen L, Martin L, Vahlne A, Zambonelli C, Barnett SW, Srivastava IK, Cheng RH - Sci Rep (2014)

Schematic representation of gp140 demonstrates intersubunit associations, relaxation of trimeric diameter upon deletion of V2.(A) The gp140 trimer was compared with the gp140ΔV2, gp140-CD4m and gp140ΔV2-CD4m maps. The degree of gp120-gp41 interface strength appears to decrease as a function of both V2 deletion and CD4m conjugation, with the gp140ΔV2-CD4m map representing the most “open” state. Inclusion of the V2 loop also results in a smaller trimeric diameter (100 Å), though the diameter remains unchanged in the gp140ΔV2, gp140-CD4m and gp140ΔV2-CD4m maps (110 Å). (B) 2D comparison of gp140ΔV2TV1 with full length constructs gp140TV1, gp140DU156.1, gp140CAP239 and gp140CAP45 reveals that full length constructs all had smaller trimeric diameters (99–103 Å) than gp140ΔV2TV1 (110 Å), indicative of closer intersubunit associations in full-length constructs than in ΔV2 constructs. Scale bar = 75 Å.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4231788&req=5

f4: Schematic representation of gp140 demonstrates intersubunit associations, relaxation of trimeric diameter upon deletion of V2.(A) The gp140 trimer was compared with the gp140ΔV2, gp140-CD4m and gp140ΔV2-CD4m maps. The degree of gp120-gp41 interface strength appears to decrease as a function of both V2 deletion and CD4m conjugation, with the gp140ΔV2-CD4m map representing the most “open” state. Inclusion of the V2 loop also results in a smaller trimeric diameter (100 Å), though the diameter remains unchanged in the gp140ΔV2, gp140-CD4m and gp140ΔV2-CD4m maps (110 Å). (B) 2D comparison of gp140ΔV2TV1 with full length constructs gp140TV1, gp140DU156.1, gp140CAP239 and gp140CAP45 reveals that full length constructs all had smaller trimeric diameters (99–103 Å) than gp140ΔV2TV1 (110 Å), indicative of closer intersubunit associations in full-length constructs than in ΔV2 constructs. Scale bar = 75 Å.
Mentions: The gp140 and gp140ΔV2 maps, with and without CD4m, were determined to have a gradient of gp120-gp41 interface “open” states, as determined by the extent of intensity at the interface region. The unliganded gp140 map had the strongest interface between gp120 and gp41 observed of all four maps, followed by the gp140ΔV2 map, then the gp140-CD4m and lastly the gp140ΔV2-CD4m map (Fig. 4A). As such, it appears that both the V2 loop and CD4m binding contribute to the degree of “open” state, putatively exposing novel epitopes at the gp120-gp41 interface region. Given the propensity of V2 to promote interprotomeric gp120-gp120 contacts via the QNE, we also observed a smaller trimeric diameter when comparing the gp140 and the gp140ΔV2 maps. The trimeric diameter remained unchanged between the gp140ΔV2, gp140-CD4m and gp140ΔV2-CD4m maps, resulting from the outward density shift promulgated by CD4m binding (Fig. 4A). Likewise, we observed that the smaller trimeric diameter is apparent in other clade C trimers, namely from the CAP45.2.00.G3, CAP239.2.00.G3J and Du156.1 strains (Fig. 4B). Measurements of trimeric diameter of ΔV2 compared to full-length strains revealed that the full length strains had smaller trimer diameters (99 to 103 Å) compared to ΔV2 (110 Å).

Bottom Line: A prominent basal quaternary location of V2 and V3' that challenges previous reports would facilitate gp41-independent gp120-gp120 interactions and suggests a quaternary mechanism of epitope occlusion facilitated by hypervariable loops.Deletion of V2 resulted in dramatic exposure of basal, membrane-proximal gp41 epitopes, consistent with its predicted basal location.The structural features of HIV-1 Env characterized here provide grounds for a paradigm shift in loop exposure and epitope occlusion, while providing substantive rationale for epitope display required for elicitation of broadly neutralizing antibodies, as well as substantiating previous pertinent literature disregarded in recent reports.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cellular Biology, University of California, Davis, CA 95616.

ABSTRACT
Hypervariable loops of HIV-1 Env protein gp120 are speculated to play roles in the conformational transition of Env to the receptor binding-induced metastable state. Structural analysis of full-length Env-based immunogens, containing the entire V2 loop, displayed tighter association between gp120 subunits, resulting in a smaller trimeric diameter than constructs lacking V2. A prominent basal quaternary location of V2 and V3' that challenges previous reports would facilitate gp41-independent gp120-gp120 interactions and suggests a quaternary mechanism of epitope occlusion facilitated by hypervariable loops. Deletion of V2 resulted in dramatic exposure of basal, membrane-proximal gp41 epitopes, consistent with its predicted basal location. The structural features of HIV-1 Env characterized here provide grounds for a paradigm shift in loop exposure and epitope occlusion, while providing substantive rationale for epitope display required for elicitation of broadly neutralizing antibodies, as well as substantiating previous pertinent literature disregarded in recent reports.

Show MeSH
Related in: MedlinePlus