Abstract

Subcellular distribution of calmodulin (CaM) in human immunodeficiency virus type-1 (HIV-1)-infected cells is distinct from that observed in uninfected cells. CaM co-localizes and interacts with the HIV-1 Gag protein in the cytosol of infected cells. Although it has been shown that binding of Gag to CaM is mediated by the matrix (MA) domain, the structural details of this interaction are not known. We have recently shown that binding of CaM to MA induces a conformational change that triggers myristate exposure, and that the CaM-binding domain of MA is confined to a region spanning residues 8-43 (MA-(8-43)). Here, we present the NMR structure of CaM bound to MA-(8-43). Our data revealed that MA-(8-43), which contains a novel CaM-binding motif, binds to CaM in an antiparallel mode with the N-terminal helix (α1) anchored to the CaM C-terminal lobe, and the C-terminal helix (α2) of MA-(8-43) bound to the N-terminal lobe of CaM. The CaM protein preserves a semiextended conformation. Binding of MA-(8-43) to CaM is mediated by numerous hydrophobic interactions and stabilized by favorable electrostatic contacts. Our structural data are consistent with the findings that CaM induces unfolding of the MA protein to have access to helices α1 and α2. It is noteworthy that several MA residues involved in CaM binding have been previously implicated in membrane binding, envelope incorporation, and particle production. The present findings may ultimately help in identification of the functional role of CaM in HIV-1 replication.

Highlights

  • Calmodulin (CaM) binds to the matrix (MA) domain of human immunodeficiency virus type-1 (HIV-1) Gag

  • Subcellular distribution of calmodulin (CaM) in human immunodeficiency virus type-1 (HIV-1)-infected cells is distinct from that observed in uninfected cells

  • It has been shown that binding of Gag to CaM is mediated by the matrix (MA) domain, the structural details of this interaction are not known

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Summary

Background

Calmodulin (CaM) binds to the matrix (MA) domain of HIV-1 Gag. Results: We present the NMR structure of CaM bound to the minimal binding domain of MA. These include the human adaptor protein complexes 1, 2, and 3 [13,14,15], tail interacting protein [16], Golgi-localized ␥-ear containing Arf-binding protein [17, 18], ADP-ribosylation factor [17], the suppressor of cytokine signaling 1 [19, 20], Lck (a lymphoid specific Src kinase) [21], N-ethylmaleimide-sensitive factor attachment protein receptor [22], Filamin A [23], vacuolar protein sorting-associated protein 18 [24], Mon2 [24], and Lyric [25] The majority of these proteins have been shown to play roles in Gag intracellular trafficking and/or assembly. These findings may help in identification of the precise functional role of CaM in HIV-1 replication

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