The sequenced genome of the poly-extremophile Exiguobacterium sp. S17, isolated from modern stromatolites at Laguna Socompa (3,570 m), a High-Altitude Andean Lake (HAAL) in Argentinean Puna revealed a putative proteorhodopsin-encoding gene. The HAAL area is exposed to the highest UV irradiation on Earth, making the microbial community living in the stromatolites test cases for survival strategies under extreme conditions. The heterologous expressed protein E17R from Exiguobacterium (248 amino acids, 85% sequence identity to its ortholog ESR from E. sibiricum) was assembled with retinal displaying an absorbance maximum at 524 nm, which makes it a member of the green-absorbing PR-subfamily. Titration down to low pH values (eventually causing partial protein denaturation) indicated a pK value between two and three. Global fitting of data from laser flash-induced absorption changes gave evidence for an early red-shifted intermediate (its formation being below the experimental resolution) that decayed (τ1 = 3.5 μs) into another red-shifted intermediate. This species decayed in a two-step process (τ2 = 84 μs, τ3 = 11 ms), to which the initial state of E17-PR was reformed with a kinetics of 2 ms. Proton transport capability of the HAAL protein was determined by BLM measurements. Additional blue light irradiation reduced the proton current, clearly identifying a blue light absorbing, M-like intermediate. The apparent absence of this intermediate is explained by closely matching formation and decay kinetics.
Planta Piloto de Procesos Industriales y Microbiológicos (PROIMI), CCT, CONICET. Av. Belgrano y Pasaje Caseros. 4000- S. M. de Tucumán, Argentina;Facultad de Ciencias Naturales e Instituto Miguel Lillo, Universidad Nacional de Tucumán, 4000, S. M. de Tucumán, Argentina;Instituto de Biología Molecular y Celular de Rosario (IBR - CONICET), Facultad de Ciencias Bioquímicas y Farmacéuticas (FBIOYF - UNR), Suipacha 590, 2000, Rosario, Santa Fe, Argentina;Max-Planck-Institute for Biophysics, Max-von-Laue-Straße 3, D-60438 Frankfurt am Main, Germany;Max-Planck-Institute for Biophysics, Max-von-Laue-Straße 3, D-60438 Frankfurt am Main, Germany;Max-Planck-Institute for Biophysics, Max-von-Laue-Straße 3, D-60438 Frankfurt am Main, Germany;Max-Planck-Institute for Biophysics, Max-von-Laue-Straße 3, D-60438 Frankfurt am Main, Germany;Max-Planck-Institute for Chemical Energy Conversion, Stiftstrasse 34–36, D-45470 Mülheim, Germany
Recommended Citation:
Virginia Helena Albarracín,Ivana Kraiselburd,Christian Bamann,et al. Functional Green-Tuned Proteorhodopsin from Modern Stromatolites[J]. PLOS ONE,2016-01-01,11(5)