Helicase Domain Containing Proteins in Human Disorders

Adayabalam   S.   Balajee; Colette      ApRhys

Abstract

Helicases are enzymes that unwind DNA-DNA and RNA-DNA duplexes play important roles in many DNA metabolic activities like replication, transcription, recombination and repair. The molecular link between helicases and genomic stability has become stronger by recent studies indicating that the genes responsible for certain human degenerative disorders such as Werner syndrome (WS), Bloom syndrome (BS) and Rothmund-Thomson syndrome (RTS) encode for helicase domain containing proteins (HDPs) homologous to bacterial RecQ super family of helicases. The patients suffering from these disorders show many signs that are suggestive of accelerated aging at an early adulthood. Some of the features include atrophy of the skin, graying of the hair, cataracts, diabetes and osteoporosis. Additionally, symptoms of accelerated aging and genomic instability have also been noticed in xeroderma pigmentosum (XP) and Cockayne syndrome (complementation group B) patients. The gene products of XP complementation groups B and D are helicases and they play dual roles both in nucleotide excision repair and RNA polymerase II transcription. The CSB protein with a remarkably conserved helicase domain is homologous to yeast SWI/SNF family of proteins that have regulatory roles in transcription, chromosome stability and DNA repair. Although genomic instability is a common feature of helicase disorders, elucidation of precise biological function(s) of helicases is critical for defining the molecular basis for diverse clinical symptoms of these patients. Recent studies have characterized the preferred DNA substrates for RecQ helicases and also identified the interaction of HDPs with a number of proteins involved in DNA replication, transcription, recombination and repair. These interactions have given great insights into functional complexities of helicases. This review deals with our current knowledge on the diverse biological functions of HDPs and their collective role in the maintenance of genomic stability.