Baculovirus IAP Research Articles

An unconventional IAP‐binding motif revealed by target‐assisted iterative screening (TAIS) of the BIR3‐cIAP1 domain

Target-assisted iterative screening (TAIS) has been applied to a random phage-displayed peptide library in a search for novel ligands of the third baculovirus IAP ('inhibitors of apoptosis') repeat (BIR) domain of cIAP1. The peptides selected in the screen fall into two distinct specificity groups, one that conforms to a known IAP-binding motif (IBM) and another one that reveals a novel BIR domain interacting motif, NH(2)-SR(V/P)W. The biochemical profiling of selected sequences with synthetic peptides, which included alanine scanning and N- and C-terminal truncations as well as competition with the Smac peptide, suggests a major energetic contribution of tryptophan at the +4 position of peptide ligands to binding and identifies the latter together with the respective pocket on the BIR domain surface as a 'hot spot' of the interaction. A peptide featuring the novel motif selectively binds the full-length cIAP1 protein in cell lysates. A 'two-pocket' model of BIR domain recognition mechanism is proposed as the basis of differential BIR domain interactions with different IBMs.

Inhibition of interleukin 1 beta-converting enzyme-mediated apoptosis of mammalian cells by baculovirus IAP.

Apoptosis can be a potent weapon against viral infection and consequently has selected for viruses carrying antiapoptosis genes. Two baculovirus proteins, IAP and p35, can prevent insect cells from dying in response to infection. p35, which interferes with members of the Ced-3 family of cysteine proteases, can also function in mammalian cells. We investigated the ability of IAP from Orgyia pseudotsugata nuclear polyhedrosis virus to prevent death of mammalian cells. IAP was transiently expressed in mammalian cells and its ability to block cell death caused by expression of interleukin-1 beta converting enzyme (ICE), FADD, or the ICE homologues ICH-1 and ICE-Lap3, was investigated. IAP strongly inhibited ICE- and ICH-1-induced cell death but protected only partially against death by overexpression of FADD and not at all against death due to enforced ICE-Lap3 expression. These results demonstrate that a baculoviral IAP protein can functionally interact with conserved components of the apoptosis machinery in mammalian cells.