ML-IAP (melanoma inhibitor of apoptosis) is a potent anti-apoptotic protein that is strongly up-regulated in melanoma and confers protection against a variety of pro-apoptotic stimuli. The mechanism by which ML-IAP regulates apoptosis is unclear, although weak inhibition of caspases 3 and 9 has been reported ...
ML-IAP (melanoma inhibitor of apoptosis) is a potent anti-apoptotic protein that is strongly up-regulated in melanoma and confers protection against a variety of pro-apoptotic stimuli. The mechanism by which ML-IAP regulates apoptosis is unclear, although weak inhibition of caspases 3 and 9 has been reported. Here, the binding to and inhibition of caspase 9 by the single BIR (baculovirus IAP repeat) domain of ML-IAP has been investigated and found to be significantly less potent than the ubiquitously expressed XIAP (X-linked IAP). Engineering of the ML-IAP-BIR domain, based on comparisons with the third BIR domain of XIAP, resulted in a chimeric BIR domain that binds to and inhibits caspase 9 significantly better than either ML-IAP-BIR or XIAP-BIR3. Mutational analysis of the ML-IAP-BIR domain demonstrated that similar enhancements in caspase 9 affinity can be achieved with only three amino acid substitutions. However, none of these modifications affected binding of the ML-IAP-BIR domain to the IAP antagonist Smac (second mitochondrial activator of caspases). ML-IAP-BIR was found to bind mature Smac with low nanomolar affinity, similar to that of XIAP-BIR2-BIR3. Correspondingly, increased expression of ML-IAP results in formation of a ML-IAP-Smac complex and disruption of the endogenous interaction between XIAP and mature Smac. These results suggest that ML-IAP might regulate apoptosis by sequestering Smac and preventing it from antagonizing XIAP-mediated inhibition of caspases, rather than by direct inhibition of caspases.
Related Citations:
Structure and Function Analysis of Peptide Antagonists of Melanoma Inhibitor of Apoptosis (ML-IAP) Franklin, M.C., Kadkhodayan, S., Ackerly, H., Alexandru, D., Distefano, M.D., Elliott, L.O., Flygare, J.A., Vucic, D., Deshayes, K., Fairbrother, W.J. (2003) Biochemistry 42: 8223
Mechanism of XIAP-mediated inhibition of caspase-9 Shizoaki, E.N., Chai, J., Rigotti, D.J., Riedl, S.J., Li, P., Srinivasula, S.M., Alnemri, E.S., Fairman, R., Shi, Y. (2003) Mol Cell 11: 519
Organizational Affiliation:
Department of Molecular Oncology, Genentech, Inc., 1 DNA Way, South San Francisco, CA 94080, USA.
Download Mendeley
