[1P-1] Poster 1 (1P-01ー1P-48)

[1P-25*] Mechanism of ATP hydrolysis in bacterial actin MreB of Spiroplasma

^○Daichi Takahashi¹, Ikuko Fujiwara^1,2, Katsumi Imada³, Makoto Miyata^1,2 (1.Grad. Sch. Sci., Osaka City Univ., 2.OCARINA, Osaka City Univ., 3.Grad. Sch. Sci., Osaka Univ.)

MreB is a bacterial actin superfamily protein. It is widely found in walled bacteria as a single copy on the genome and forms double-stranded filaments to function as a scaffold for the peptidoglycan synthesis complex. However, Spiroplasma has five MreBs (MreB1-5) to drive the swimming motility. MreB3 releases P_i at a much slower rate than other MreBs. To elucidate the mechanism underlying the slow P_i release rate, we analyzed the crystal structure of MreB3 in complex with AMPPNP. K174, which corresponds to the conserved Thr that interacts with the nucleophilic water for the attack on the γ-phosphate in other MreBs, did not form a hydrogen bond with the putative nucleophilic water in MreB3. The acidic residue that interacts with the conserved Thr in other MreBs is substituted by Ser (S176) in MreB3. The P_i release rate of the K174T/S176D double mutant variant of MreB3 was 11 times higher than that of wild type MreB3, although that of each single mutant (MreB3 K174T and S176D) was similar to the wild type one. These results suggest that the lack of the proton pathway composed of Thr and an acidic residue causes the slow P_i release rate of MreB3.