期刊
BIOCHEMISTRY
卷 45, 期 8, 页码 2729-2738出版社
AMER CHEMICAL SOC
DOI: 10.1021/bi051682b
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资金
- NIAMS NIH HHS [AR 048526, AR 048898] Funding Source: Medline
- NIDCD NIH HHS [DC 006103] Funding Source: Medline
There are three isoforms of class V myosin in mammals. While myosin Va has been studied well, little is known about the function of other myosin V isoforms (Vb and Vc) at a molecular level. Here we report the mechanoenzymatic function of human myosin Vb (HuM5B) for the first time. Electron microscopic observation showed that HuM5B has a double-headed structure with a long neck like myosin Va. V-max and K-actin of the actin-activated ATPase activity of HuM5B were 9.7 +/- 0.4 s(-1) and 8.5 +/- 0.1 mu M, respectively. K-actin and K-ATP of the actin-activated ATPase activity were significantly higher than those of myosin Va. ADP markedly inhibited the ATPase activity. The rate of release of ADP from acto-HuM5B was 12.2 +/- 0.5 s(-1), which was comparable to the V-max, of the actin-activated ATPase activity. These results suggest that ADP release is the rate-limiting step for the actin-activated ATPase cycle; thus, HuM5B is a high duty ratio myosin. Consistently, the actin gliding velocity (0.22 +/- 0.03 mu m/s) remained constant at a low motor density. The actin filament landing assay revealed that a single HuM5B molecule is sufficient to move the actin filament continuously, indicating that HuM5b is a processive motor.
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