Department of Microbiology & Immunology, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
PLoS One. 2021 Feb 4;16(2):e0246212. doi: 10.1371/journal.pone.0246212. eCollection 2021.
Bacterial species of the genera Agrobacterium and Borrelia possess chromosomes terminated by hairpin telomeres. Replication produces dimeric replication intermediates fused via replicated telomere junctions. A specialized class of enzymes, referred to as telomere resolvases, promotes the resolution of the replicated intermediate into linear monomers terminated by hairpin telomeres. Telomere resolution is catalyzed via DNA cleavage and rejoining events mechanistically similar to those promoted by topoisomerase-IB and tyrosine recombinase enzymes. Examination of the borrelial telomere resolvase, ResT, revealed unanticipated multifunctionality; aside from its expected telomere resolution activity ResT possessed a singled-stranded DNA (ssDNA) annealing activity that extended to both naked ssDNA and ssDNA complexed with its cognate single-stranded DNA binding protein (SSB). At present, the role this DNA annealing activity plays in vivo remains unknown. We have demonstrated here that single-stranded DNA annealing is also a conserved property of the agrobacterial telomere resolvase, TelA. This activity in TelA similarly extends to both naked ssDNA and ssDNA bound by its cognate SSB. TelA's annealing activity was shown to stem from the N-terminal domain; removal of this domain abolished annealing without affecting telomere resolution. Further, independent expression of the N-terminal domain of TelA produced a functional annealing protein. We suggest that the apparent conservation of annealing activity in two telomere resolvases, from distantly related bacterial species, implies a role for this activity in hairpin telomere metabolism. Our demonstration of the separation of the telomere resolution and annealing activities of TelA provides a platform for future experiments aimed at identifying the role DNA annealing performs in vivo.
细菌属的农杆菌和螺旋体属的细菌具有发夹状端粒的染色体。复制产生通过复制的端粒连接融合的二聚体复制中间体。一类称为端粒内切酶的特殊酶类，促进复制中间体通过 DNA 切割和连接事件解旋为发夹状端粒终止的线性单体，该过程类似于拓扑异构酶 IB 和酪氨酸重组酶促进的过程。对螺旋体端粒内切酶 ResT 的研究揭示了其出乎意料的多功能性；除了预期的端粒分辨率活性外，ResT 还具有单链 DNA（ssDNA）退火活性，可延伸至裸露的 ssDNA 和与其同源单链 DNA 结合蛋白（SSB）结合的 ssDNA。目前，这种 DNA 退火活性在体内的作用尚不清楚。我们在这里证明，ssDNA 退火也是农杆菌端粒内切酶 TelA 的保守特性。TelA 的这种活性同样适用于裸露的 ssDNA 和与其同源 SSB 结合的 ssDNA。TelA 的退火活性源自 N 端结构域；去除该结构域会破坏退火而不影响端粒分辨率。此外，TelA 的 N 端结构域的独立表达产生了具有功能的退火蛋白。我们认为，两个亲缘关系较远的细菌属的端粒内切酶中退火活性的明显保守性意味着该活性在发夹状端粒代谢中具有作用。我们对 TelA 的端粒分辨率和退火活性的分离的证明，为今后旨在确定 DNA 退火在体内所起作用的实验提供了一个平台。
