Abstract
ResT is the telomere resolvase of the spirochete Borrelia burgdorferi, the causative agent of Lyme disease. ResT is an essential cellular function that processes replication intermediates to produce linear replicons terminated by covalently closed hairpin telomeres. ResT generates these hairpin telomeres in a reaction with mechanistic similarities to those catalyzed by type IB topoisomerases and tyrosine recombinases. We report here, that like most of the tyrosine recombinases, ResT requires interprotomer communication, likely in an in-line synapse, to activate reaction chemistry. Unlike the tyrosine recombinases, however, we infer that the cleavage and strand transfer reactions on the two sides of the replicated telomere occur nearly simultaneously. Nonetheless, the chemical steps of the forward and reverse reactions performed by ResT can occur in a non-concerted fashion (i.e. events on the two sides of the replicated telomere can occur independently). We propose that uncoupling of reaction completion on the two sides of the substrate is facilitated by an early commitment to hairpin formation that is imposed by the precleavage action of the hairpin binding module of the ResT active site.
Highlights
Spirochetes of the genus Borrelia are important human pathogens that cause Lyme disease [3, 4] and relapsing fever [5]
Telomere resolution by ResT proceeds by a two-step transesterification involving an active site tyrosine (Tyr335) that proceeds with the same polarity as that of the type IB topoisomerases and the site-specific recombinase class referred to as tyrosine recombinases [11, 16]
Nucleophilic attack by the active site tyrosine, on phosphodiester bonds separated by 6 bp on the opposite DNA strands in the replicated telomere, produces a transient covalent 3Ј-phosphotyrosyl-ResT intermediate
Summary
Spirochetes of the genus Borrelia are important human pathogens (see [1, 2]) that cause Lyme disease [3, 4] and relapsing fever [5]. The Borrelia species possess intriguing genomes in that they are highly segmented with most of their replicons being linear DNAs terminated by covalently closed DNA hairpins, referred to as telomeres (see Ref. 6). Nucleophilic attack by the active site tyrosine, on phosphodiester bonds separated by 6 bp on the opposite DNA strands in the replicated telomere, produces a transient covalent 3Ј-phosphotyrosyl-ResT intermediate. Subsequent nucleophilic attack of the phosphotyrosyl linkage by the 5Ј-hydroxyl group of the opposite DNA strand displaces the resolvase and results in the formation of covalently closed hairpin telomeres (Fig. 1A, top panel). ResT can run the reverse reaction (Fig. 1A, bottom panel) in which hairpin telomeres are fused together, an activity believed to generate telomere exchanges and gene duplications among the linear replicons of B. burgdorferi [17]
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