Biochemical Characterization of a Recombinant TRIM5α Protein That Restricts Human Immunodeficiency Virus Type 1 Replication

Abstract

The rhesus monkey intrinsic immunity factor TRIM5␣ rh recognizes incoming capsids from a variety of retroviruses, including human immunodeficiency virus type 1 (HIV-1) and equine infectious anemia virus (EIAV), and inhibits the accumulation of viral reverse transcripts. However, direct interactions between restricting TRIM5␣ proteins and retroviral capsids have not previously been demonstrated using pure recombinant proteins. To facilitate structural and mechanistic studies of retroviral restriction, we have developed methods for expressing and purifying an active chimeric TRIM5␣ rh protein containing the RING domain from the related human TRIM21 protein. This recombinant TRIM5-21R protein was expressed in SF-21 insect cells and purified through three chromatographic steps. Two distinct TRIM5-21R species were purified and shown to correspond to monomers and dimers, as analyzed by analytical ultracentrifugation. Chemically cross-linked recombinant TRIM5-21R dimers and mammalian-expressed TRIM5-21R and TRIM5␣ proteins exhibited similar sodium dodecyl sulfate-polyacrylamide gel electrophoresis mobilities, indicating that mammalian TRIM5␣ proteins are predominantly dimeric. Purified TRIM5-21R had ubiquitin ligase activity and could autoubquitylate with different E2 ubiquitin conjugating enzymes in vitro. TRIM5-21R bound directly to synthetic capsids composed of recombinant HIV-1 CA-NC proteins and to authentic EIAV core particles. HIV-1 CA-NC assemblies bound dimeric TRIM5-21R better than either monomeric TRIM5-21R or TRIM5-21R constructs that lacked the SPRY domain or its V1 loop. Thus, our studies indicate that TRIM5␣ proteins are dimeric ubiquitin E3 ligases that recognize retroviral capsids through direct interactions mediated by the SPRY domain and demonstrate that these activities can be recapitulated in vitro using pure recombinant proteins.Susceptibility to retroviral infections influences species survival and has driven the evolution of cellular restriction factors that inhibit retroviral replication. One important antiretroviral intrinsic immune response is mediated by TRIM5␣, which can block early postentry steps in the replication of certain retroviruses in specific primate lineages (3, 37, 55, 58). Under normal restrictive conditions, TRIM5␣ proteins block accumulation of retroviral reverse transcripts (55) and accelerate the rate at which viral capsids dissociate from high-molecularweight complexes into lower-molecular-weight subunits (42,56). The allelic specificity of TRIM5␣ restriction is illustrated by the fact that rhesus macaque TRIM5␣ potently inhibits human immunodeficiency virus type 1 (HIV-1) replication, whereas human TRIM5␣ instead exhibits restriction activity against N-tropic murine leukemia virus but not 29,43,55,67). These differences can be attributed to the differential abilities of TRIM5␣ proteins to interact with retroviral capsids after viral entry (34,42,56).Like other tripartite (TRIM) family members, TRIM5␣ contains RING, B-box, coiled-coil, and B30.2/SPRY domains, and each of t...

Structural insight into HIV-1 capsid recognition by rhesus TRIM5α

“…It has been shown that a full-length TRIM5α chimera (TRIM5Rh-21R) exists as a mixture of monomers and dimers whereas a truncated TRIM5α (CC-SPRY) is a dimer (11,23,24). We investigated the oligomerization state of PRY/SPRY rh and PRY/SPRY hu .…”

“…We performed further dissection of the TRIM5α-CA interaction to address the mechanistic question of whether the PRY/SPRY rh domain alone is sufficient to recognize the HIV-1 capsid. It had been demonstrated previously that rhTRIM5α (11,37) and its truncation containing the coiled-coil and PRY/SPRY domains (23) can bind and disrupt HIV-1 CA/CA-NC assembled into tubes or purified viral cores. We used monomeric MBP-PRY/SPRY rh (24 μM) or MBP-PRY/SPRY hu (21 μM) in a precipitation assay (23) with preassembled CA tubes (69 μM).…”

“…1A), similar to many tripartite/ RBCC motif (TRIM) family members (7). The RING domain functions as an E3 ubiquitin ligase (8); the B-box 2 domain mediates formation of higher-order structure and self-association (9,10); and the coiled-coil domain mediates dimerization (11) and facilitates the formation of the hexagonal lattice (12). The PRY/SPRY domain is essential for recognition of retroviral capsids and determines the specificity of restriction (13,14).…”

Using Antiubiquitin Antibodies to Probe the Ubiquitination State Within rhTRIM5α Cytoplasmic Bodies

“…[2][3][4] This SPRY domain interacts with the capsid core of the virus, and in the case of the rhesus macaque variant of TRIM5a (rhTRIM5a), interaction with the capsid core of HIV-1 normally leads to a block in infectivity prior to the completion of reverse transcription. [5][6][7] Members of the TRIM family of proteins have been shown to self-associate through coiled-coiled domains into higherorder oligomers, [8][9][10] and many members of this family accumulate in discrete subcellular structures. 11 Studies examining the subcellular localization of rhTRIM5a revealed that this protein localizes in two cytoplasmic populations, but these populations are dynamic and are capable of exchanging protein.…”

Modulation of TRIM5α Activity in Human Cells by Alternatively Spliced TRIM5 Isoforms

“…The function of the B-box 2 domain (coded by exon 2) is not fully understood, but amino acid changes in this region can influence TRIM5␣ turnover, higherorder self-association of TRIM5␣ dimers, the formation of TRIM5␣-containing cytoplasmic bodies, and antiviral activity (7,10,15,20). The coiled-coil domain (coded by exons 2 to 4) promotes the formation of homodimers and participates in capsid recognition (16,19,24,26,30). These three domains comprise the RING/B-box/coiled-coil (RBCC) tripartite motif characteristic of all TRIM proteins.…”