Structural basis of the protochromic green/red photocycle of the chromatic acclimation sensor RcaE
T. Nagae, Masashi Unno, T. Koizumi, Yohei Miyanoiri, Tomotsumi Fujisawa, Kento Masui, Takanari Kamo, Kei Wada, Toshihiko Eki, Yutaka Ito, Yuu Hirose, Masaki Mishima
Abstract
, whereas they are directly hydrogen bonded in the β-face with the carboxyl group of Glu217. Glu217 is further connected to a cluster of waters forming a hole in the bucket, which are in exchange with solvent waters in molecular dynamics simulation. We propose that the "leaky bucket" structure functions as a proton exit/influx pathway upon photoconversion. NMR analysis demonstrated that the four pyrrole nitrogen atoms are indeed fully protonated in the red-absorbing state, but one of them, most likely the B-ring nitrogen, is deprotonated in the green-absorbing state. These findings deepen our understanding of the diverse spectral tuning mechanisms present in CBCRs.