Evolutionary origins of membrane proteins Armen Y. Mulkidjanian 1,2,* , and Michael Y. Galperin 3 1 School of Physics, University of Osnabrück, D-49069 Osnabrück, Germany, 2 A.N.Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, 119991, Russia, and 3 National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA * To whom correspondence should be addressed E-mail: amulkid@uos.de