||January, 19, 2009 |
||Dr. Paul Horton, Team Leader, Computational Biology Research Center,
||Mitochondrial β-Barrel Proteins, an Exclusive Club?
In this talk I will introduce recent experimental and bioinformatics
results which have changed our view of the mitochondrial outer
Mitochondria are believe to have evolved from ancestors of the
alphaproteobacteria, which have outer membranes populated by numerous
proteins, exclusively of beta-barrel architecture, representing 2-3%
of their proteomes. In the light of this fact and some preliminary
analysis, mitochondria were expected to have perhaps 100 Mitochondrial
beta-barrel Outer Membrane Proteins (MBOMPs) (Wimley 2003). In
contrast to that expectation, and despite the availability of whole
genome sequences for several eukaryotes, only 5 types of MBOMPs have
been identified (Tom40, Porin, Mdm10, Sam50 and Mmm2). Moreover, the
sequence characteristics reponsible for localization and membrane
integration of these proteins was unknown.
Recently a breakthrough was reported by (Kutik et al., 2008), who
discovered a C-terminal region signal sequence Po.G..Hy.Hy, (Po =
polar, Hy = large hydrophobic residue) which they named the
beta-signal. They showed the experimentally that 3 of the 5 known
MBOMPs posess and require this signal, and argued from evolutionary
conservation that a 4th MBOMP also possesses a functional beta-signal.
Our group considered the newly discovered beta-signal as an
opportunity to search the genome for the "missing" MBOMP's expected to
be lurking in the proteome. To our surprise, insteading of finding
multiple new candidates (we did identify one candidate which is
currently being tested by a collaborator), we instead found indirect
but convincing evidence that the estimated number of MBOMP's should
probably be reduced by an order of magnitude. In my talk I will
discuss the results of our informatics analysis of the mitochondrial
proteome in light of the beta-signal and the recently announced NMR
structure of human VDAC-1 (Hiller et al. 2008).
1. Imai, K., Gromiha, M. and Horton, P. (2008). Cell 135(7), 1158-9.
2. Kutik, S., Stojanovski, D., Becker, L., Becker, T., Meinecke, M., Krueger, V., Prinz, C., Meisinger, C., Guiard, B., Wanger, R., Pfanner, N., and Weidermann N. (2008). cell 132, 1011-1024.
3. Neupert, W., and Herrmann, J. (2007), Annu. Rev. Biochem. 76, 723-749.
4. Hiller, S., Garces, R., Malia, T., Orekhov, V., Colombini, M., and Wagner, G. (2008). Science 321, 1206-1210.
5. White, S. (2008), Membrane Proteins of Known 3D Structure, http://blanco.biomol.uci.edu/Membrane_Proteins_xtal.html
6. Wimley, W. (2003), Curr. Opin. Struct. Biol., 13, 404-411.