Novel modular domain PB1 recognizes PC motif to mediate functional protein–protein interactions

Takashi Ito¹, Yasushi Matsui², Tetsuro Ago^3,4, Kazuhisa Ota, and Hideki Sumimoto^1,3,4

Division of Genome Biology, Cancer Research Institute, Kanazawa University, 13-1 Takaramachi, Kanazawa 920-0934, ²Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, ³Department of Molecular and Structural Biology, Kyushu University Graduate School of Medical Science, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582 and ⁴Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan ¹Corresponding authors e-mail: titolab{at}kenroku.kanazawa-u.ac.jp or hsumi{at}mailserver.med.kyushu-u.ac.jp

Abstract: Modular domains mediating specific protein–protein interactions play central roles in the formation of complex regulatory networks to execute various cellular activities. Here we identify a novel domain PB1 in the budding yeast protein Bem1p, which functions in polarity establishment, and mammalian p67^phox, which activates the microbicidal phagocyte NADPH oxidase. Each of these specifically recognizes an evolutionarily conserved PC motif to interact directly with Cdc24p (an essential protein for cell polarization) and p40^phox (a component of the signaling complex for the oxidase), respectively. Swapping the PB1 domain of Bem1p with that of p67^phox, which abolishes its interaction with Cdc24p, confers on cells temperature- sensitive growth and a bilateral mating defect. These phenotypes are suppressed by a mutant Cdc24p harboring the PC motif-containing region of p40^phox, which restores the interaction with the altered Bem1p. This domain-swapping experiment demonstrates that Bem1p function requires interaction with Cdc24p, in which the PB1 domain and the PC motif participate as responsible modules.

Key Words: Keywords: Bem1p/Cdc24p/cell polarity/NADPH oxidase/p67^phox