Abstract
After entry into target cells, retroviruses encounter the host restriction factors such as Fv1 and TRIM5α. While it is clear that these factors target retrovirus capsid proteins (CA), recognition remains poorly defined in the absence of structural information. To better understand the binding interaction between TRIM5α and CA, we selected a panel of novel N-tropic murine leukaemia virus (N-MLV) escape mutants by a serial passage of replication competent N-MLV in rhesus macaque TRIM5α (rhTRIM5α)-positive cells using a small percentage of unrestricted cells to allow multiple rounds of virus replication. The newly identified mutations, many of which involve changes in charge, are distributed over the outer ‘top’ surface of N-MLV CA, including the N-terminal β-hairpin, and map up to 29 Ao apart. Biological characterisation with a number of restriction factors revealed that only one of the new mutations affects restriction by human TRIM5α, indicating significant differences in the binding interaction between N-MLV and the two TRIM5αs, whereas three of the mutations result in dual sensitivity to Fv1n and Fv1b. Structural studies of two mutants show that no major changes in the overall CA conformation are associated with escape from restriction. We conclude that interactions involving much, if not all, of the surface of CA are vital for TRIM5α binding.
Highlights
Mammalian cells show different susceptibilities to retrovirus infection
Host restriction factors such as TRIM5a are important for preventing cross species transmission of a variety of retroviruses
They act to block viral replication but their mode of virus recognition is poorly understood. To address this question we have developed a procedure for isolating viruses that replicate in the presence of restriction factors
Summary
Cells from mice exhibit different susceptibility to murine leukaemia virus (MLV) dependent on their genetic backgrounds; cell lines from different primates show defined patterns of lentiviral replication In many cases, these variations are due to the presence of cellular proteins referred as restriction factors. The a isoform of TRIM5 (TRIM5a) has an additional large B30.2 or PRYSPRY domain at its Cterminus [11,12], important for recognizing the viral target [13,14,15,16] Both Fv1 [17,18] and TRIM5a [5,19] target the viral capsid protein (CA), blocking retrovirus replication after viral entry into the target cell. Restriction by TRIM5a, is clearly distinguished from that by Fv1 in that TRIM5a-mediated restriction normally occurs before or during reverse transcription [5,20], whereas Fv1-mediated restriction occurs after the completion of reverse transcription but prior to viral integration [21,22]
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