Specificity of Interactions among the DNA-packaging Machine Components of T4-related Bacteriophages

Song Gao,Venigalla B Rao

doi:10.1074/jbc.m110.196907

Abstract

Tailed bacteriophages use powerful molecular motors to package the viral genome into a preformed capsid. Packaging at a rate of up to ∼2000 bp/s and generating a power density twice that of an automobile engine, the phage T4 motor is the fastest and most powerful reported to date. Central to DNA packaging are dynamic interactions among the packaging components, capsid (gp23), portal (gp20), motor (gp17, large "terminase"), and regulator (gp16, small terminase), leading to precise orchestration of the packaging process, but the mechanisms are poorly understood. Here we analyzed the interactions between small and large terminases of T4-related phages. Our results show that the gp17 packaging ATPase is maximally stimulated by homologous, but not heterologous, gp16. Multiple interaction sites are identified in both gp16 and gp17. The specificity determinants in gp16 are clustered in the diverged N- and C-terminal domains (regions I-III). Swapping of diverged region(s), such as replacing C-terminal RB49 region III with that of T4, switched ATPase stimulation specificity. Two specificity regions, amino acids 37-52 and 290-315, are identified in or near the gp17-ATPase "transmission" subdomain II. gp16 binding at these sites might cause a conformational change positioning the ATPase-coupling residues into the catalytic pocket, triggering ATP hydrolysis. These results lead to a model in which multiple weak interactions between motor and regulator allow dynamic assembly and disassembly of various packaging complexes, depending on the functional state of the packaging machine. This might be a general mechanism for regulation of the phage packaging machine and other complex molecular machines.

Highlights

Phage T4 packages its 171-kb, 56-␮m-long genome into a capsid shell that is 120 nm long and 86 nm wide [4]
The packaging machine consists of a small terminase, gp16 (18 kDa), which is essential for DNA packaging in vivo [14], 2 The term “terminase” was originally used to refer to the enzyme activity that generates the termini of virion DNA
Small and Large Terminase Interactions in Phage T4 but in vitro, where DNA translocation can be measured independent of other steps, the motor can function without gp16 [15,16,17]. gp16 forms oligomeric “rings,” each ring consisting of 8 –11 subunits (18 –20)

Summary

Introduction

Phage T4 packages its 171-kb, 56-␮m-long genome into a capsid shell that is 120 nm long and 86 nm wide [4]. C-terminal Region III Is the Most Essential for ATPase Stimulation Specificity—A series of swap mutants were constructed by exchanging one or more of the diverged regions from one phage gp16 with another (Fig. 6A).

Results

Conclusion