SPECIFIC PERSULFIDE SENSING MECHANISM OF A THIOL BASED TRANSCRIPTIONAL REGULATOR

GONZALEZ-GUTIERREZ, GIOVANNI; ZHANG, YIFAN; CAPDEVILA, DAIANA A; GIEDROC, DAVID P

Eugene, Oregon

Conferencia; II American Gasotranmitter Conference; 2019

Oregon state university

Sulfide was used as an electron donor early in the evolution of photosynthesis,many bacteria are still capable of using sulfur compounds such as hydrogensulfide (H 2 S) as a photosynthetic electron donor. Although enzymes involved inH 2 S oxidation have been characterized, mechanisms of regulation of sulfide-dependent photosynthesis have not been elucidated. Here we present a structuraland mechanistic study on a sulfide-responsive transcriptional repressor, SqrR,that functions as a master regulator of sulfide-dependent gene expression in thepurple photosynthetic bacterium Rhodobacter capsulatus. SqrR is a ArsR familymember that when incubated with a organic persulfide donora, glutathionepersulfide (GSSH) and cysteine trisulfide (CSSSC), reduced SqrR is converted toa tetrasulfide-crosslinked species (+62 amu), which gives rise to negativeregulation of DNA binding, inducing the expression of sulfide-responsive genes(1). We conducted an extensive crystallographic study of SqrR and have solvedthe crystal structures of the reduced, disulfide and tetrasulfide crosslinked SqrRs.This includes, to our knowledge, the first crystal structure of a tetrasulfidecrosslink within proteins. These high-resolution structures suggest that chemistryof this sensor is determined by local steric hindrance that impairs simple disulfidechemistry, additionally we show that the disulfide formation is impaired by a highenthalpic cost. Using a combination of ratiometric pulsed alkylation-massspectrometry and site-directed mutagenesis we study the kinetics of the formationof tetrasulfide bridge.