Roles of the C-Terminal Amino Acids of Non-Hexameric Helicases: Insights from Escherichia coli UvrD.

Hiroaki Yokota

doi:10.3390/ijms22031018

Abstract

Helicases are nucleic acid-unwinding enzymes that are involved in the maintenance of genome integrity. Several parts of the amino acid sequences of helicases are very similar, and these quite well-conserved amino acid sequences are termed “helicase motifs”. Previous studies by X-ray crystallography and single-molecule measurements have suggested a common underlying mechanism for their function. These studies indicate the role of the helicase motifs in unwinding nucleic acids. In contrast, the sequence and length of the C-terminal amino acids of helicases are highly variable. In this paper, I review past and recent studies that proposed helicase mechanisms and studies that investigated the roles of the C-terminal amino acids on helicase and dimerization activities, primarily on the non-hexermeric Escherichia coli (E. coli) UvrD helicase. Then, I center on my recent study of single-molecule direct visualization of a UvrD mutant lacking the C-terminal 40 amino acids (UvrDΔ40C) used in studies proposing the monomer helicase model. The study demonstrated that multiple UvrDΔ40C molecules jointly participated in DNA unwinding, presumably by forming an oligomer. Thus, the single-molecule observation addressed how the C-terminal amino acids affect the number of helicases bound to DNA, oligomerization, and unwinding activity, which can be applied to other helicases.

Highlights

Helicases are enzymes that unwind nucleic acids using energy derived from NTP hydrolysis and fulfill essential functions in the maintenance of genome integrity, includingDNA replication, repair, and recombination
The seven helicase motifs of SF1 and SF2 helicases, which are essential to adenosine triphosphate (ATP) hydrolysis and nucleic acid binding and unwinding, are commonly placed in the middle of the amino acid sequences
Showed americ helicases such as RecQ [26] and Dda [36]. This model was built based on the notion that the 2B domain of the UvrD that first bound to DNA was altered to a more closed that multiple helicases participate in DNA unwinding, but they unwind DNA without conformation by the binding of a second UvrD to the first bound UvrD, actiself-interaction or oligomerization

Summary

Introduction

Helicases are enzymes that unwind nucleic acids using energy derived from NTP hydrolysis and fulfill essential functions in the maintenance of genome integrity, including. The number of conserved helicase motifs for SF1 and SF2 is at least seven, and they share common sequences [2] These conserved motifs, which are essential to adenosine triphosphate (ATP) hydrolysis and nucleic acid binding and unwinding, are commonly placed not at N- and C-termini, but in the middle of the amino acid sequences. I review past and recent studies that proposed helicase mechanisms and studies that investigated the roles of the C-terminal amino acids of helicase and dimerization activities, primarily on the non-hexermeric Escherichia coli (E. coli) SF1 UvrD helicase. The results should settle the controversy of the monomer/oligomer helicase models, address the role of C-terminal amino acids in binding and unwinding DNA, and elucidate their effects on helicase and dimerization activities

Helicase Superfamily

Superfamily 1 Helicases

Structural

Superfamily 2 Helicases

Proposed Models for the Functional Unit of Some SF1 and SF2 Helicases

C-Terminal Amino Acids

C-Terminus Truncated UvrD

Experiments

Single-molecule visualization

Transient

Findings

Summary