Nanomotors in nanotechnology may be as important as cars in daily life. Biomotors are nanoscale machines ubiquitous in living systems to carry out ATP-driven activities such as walking, breathing, blinking, mitosis, replication, transcription, and trafficking. The sequential action in an asymmetrical hexamer by a revolving mechanism has been confirmed in dsDNA packaging motors of phi29, herpesviruses, bacterial dsDNA translocase FtsK, and Streptomyces TraB for conjugative dsDNA transfer. These elaborate, delicate, and exquisite ring structures have inspired scientists to design biomimetics in nanotechnology. Many multisubunit ATPase rings generate force via sequential action of multiple modules, such as the Walker A, Walker B, P-loop, arginine finger, sensors, and lid. The chemical to mechanical energy conversion usually takes place in sequential order. It is commonly believed that ATP binding triggers such conversion, but how the multimodule motor starts the sequential process has not been explicitly investigated. Identification of the starter is of great significance for biomimetic motor fabrication. Here, we report that the arginine finger is the starter of the motor. Only one amino acid residue change in the arginine finger led to the impediment and elimination of all following steps. Without the arginine finger, the motor failed to assemble, bind ATP, recruit DNA, or hydrolyze ATP and was eventually unable to package DNA. However, the loss of ATPase activity due to an inactive arginine finger can be rescued by an arginine finger from the adjacent subunit of Walker A mutant through trans-complementation. Taken together, we demonstrate that the formation of dimers triggered by the arginine finger initiates the motor action rather than the general belief of initiation by ATP binding.
Keywords: DNA-packaging motor; asymmetrical hexameric ATPase; inchworm; phi29 DNA packaging; revolving motor; sequential action; viral assembly.