AbstractsBiology & Animal Science

Retrovirus-Specific Differences in Matrix (MA) and Nucleocapsid (NC) Protein-Nucleic Acid Interactions: Implications for Genomic RNA Packaging

by Meng Sun




Institution: The Ohio State University
Department: Chemistry
Degree: PhD
Year: 2012
Keywords: Biochemistry; retrovirus; matrix; nucleocapsid; genome packaging
Record ID: 1974897
Full text PDF: http://rave.ohiolink.edu/etdc/view?acc_num=osu1343844761


Abstract

Retroviral RNA encapsidation involves a recognition event between genomic RNA packaging signals and one or more domains in Gag. In human immunodeficiency virus type 1 (HIV-1), the nucleocapsid (NC) protein domain of Gag is known to be involved in genomic RNA packaging, and displays robust nucleic acid binding, aggregation, and chaperone functions. By comparison, human T-cell leukemia virus type 1 (HTLV-1) NC, a member of the deltaretrovirus genus, displays weaker nucleic acid binding affinity and very little chaperone or aggregation activity. It has also been demonstrated that mutation of conserved charged residues in the bovine leukemia virus (BLV) matrix (MA) domain affects virus replication and viral RNA packaging efficiencies in cell-based assays. Based on these observations, we hypothesized that the MA domain of Gag may generally contribute to nucleic acid binding and genome encapsidation for the deltaretroviruses. To gain further insight into the nucleic acid binding properties of MA, we examined the interaction between HTLV-2 and HIV-1 MA proteins and various nucleic acid constructs in vitro . Mutagenesis studies were designed to probe the role of conserved charged and aromatic amino acid residues of MA in aggregating and binding nucleic acids. In general, HTLV-2 MA displays higher binding affinity to nucleic acids and better chaperone and aggregation activities than HIV-1 MA; SL2 binding is less salt-sensitive than ssDNA binding. HTLV-2 MA bound NAs with higher affinity than HTLV-2 NC, and displays more robust chaperone function. The simultaneous mutation of two basic residues in HTLV-2 MA a-helix II, previously implicated in BLV viral RNA packaging, dramatically reduces NA binding affinity. HTLV-2 MA binds with higher affinity to SL2 RNA derived from the putative packaging signal of HTLV-2 relative to nonspecific ssDNA. Furthermore, an HIV-1 MA triple mutant, E40R/E42L/N47K, designed to mimic the basic character of HTLV-2 MA a-helix II, dramatically improves binding affinity and chaperone activity of the HIV-1 MA protein in vitro and restores RNA packaging to a ¿NC HIV-1 variant in vivo . Taken together, these results are consistent with a role for deltaretrovirus MA proteins in viral RNA packaging.