Nature：同聚环ATP酶协调ATP水解及机制功能的方式

同聚环ATP酶见于所有生命形式中，参与很多过程，如染色体分离、蛋白解折叠和ATP合成。这种引人注目的功能多样性是由一个高度保留的结构核产生的，该结构核负责ATP的结合和水解。但这些酶是怎样协调ATP水解及机制功能的却基本不清楚。其中一种这样的环ATP酶来自一种名为phi29的噬菌体，它帮助将dsDNA基因组加载到病毒壳中。

在最新一期Nature上面，Moffitt等人发现，这一由5部分组成的运动机制将DNA包装在由10个碱基对组成的“爆发” 中，每个“爆发”由4个包含2.5个碱基对的步骤组成，每个步骤相应于每个ATP的水解。这样一个非整步的大小是前所未有的，它提出了关于环内ATP水解及ATP环与DNA相互作用的有趣的机制问题。

Nature 457, 446-450 (22 January 2009) | doi:10.1038/nature07637

Intersubunit coordination in a homomeric ring ATPase

Jeffrey R. Moffitt1,6, Yann R. Chemla1,6,7, K. Aathavan2, Shelley Grimes3, Paul J. Jardine3, Dwight L. Anderson3,4 & Carlos Bustamante1,2,5

1 Department of Physics and Jason L. Choy Laboratory of Single Molecule Biophysics,
2 Biophysics Graduate Group, University of California, Berkeley, California 94720, USA
3 Department of Diagnostic and Biological Sciences,
4 Department of Microbiology, University of Minnesota, Minneapolis, Minnesota 55455, USA
5 Departments of Molecular and Cell Biology, Chemistry, and Howard Hughes Medical Institute, University of California, Berkeley, California 94720, USA
6 These authors contributed equally to this work.

Homomeric ring ATPases perform many vital and varied tasks in the cell, ranging from chromosome segregation to protein degradation. Here we report the direct observation of the intersubunit coordination and step size of such a ring ATPase, the double-stranded-DNA packaging motor in the bacteriophage 29. Using high-resolution optical tweezers, we find that packaging occurs in increments of 10 base pairs (bp). Statistical analysis of the preceding dwell times reveals that multiple ATPs bind during each dwell, and application of high force reveals that these 10-bp increments are composed of four 2.5-bp steps. These results indicate that the hydrolysis cycles of the individual subunits are highly coordinated by means of a mechanism novel for ring ATPases. Furthermore, a step size that is a non-integer number of base pairs demands new models for motor–DNA interactions.