Compensation for L212GLU in bacterial reaction centers
- Argonne National Lab., IL (United States)
- Centre de Genetique Moleculaire, Gif/Yvette (France). CNRS
In wild-type bacterial reaction centers (RC), residue L212Glu, which is located about 5 {Angstrom} away from Q{sub B}, is involved in the delivery of the second proton to Q{sub B{sup 2}{minus}} [1-4]. We previously constructed the L212Glu-L213Asp {yields} Ala-Ala double mutant of Rhodobacter capsulatus, and it is incapable of photosynthetic growth (PS{sup {minus}}) due to interruption of the proton transfer pathway to Q{sub B}[3,4]. We have isolated several photocompetent (PS{sup +}) phenotypic revertants of this L212-L213AA double mutant [3-7]. The compensatory mutations that restore function in these strains are diverse and show that neither L212Glu nor L213Asp is absolutely required for efficient light-induced electron or proton transfer. Genotypic revertant and second-site mutations, located within the Q{sub B} binding picket or at more distant sites, can compensate for mutations at L212 and L213 to restore photocompetence. One of the phenotypic revertants of the L212Ala-L213Ala double mutant carries a genotypic reversion of L213Ala to Asp; the Ala substitution at L212 remains. We were intrigued that this L212Glu {yields} Ala mutant R. capsulatus is photocompetent, while the L212Glu {yields} Gln mutant of R. sphaeroides is not, particularly since the sequence identity in the Q{sub B} site of these two strains is 90{percent} [8]. To this end, we constructed the L212Glu {yields} Gln mutant in R. capsulatus, and it is also PS{sup {minus}}. To determine the function that is lost in the L212Gln mutant but restored by Ala at that site, we selected four PS{sup +} revertants from the L212Gln strain.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- W-31109-ENG-38
- OSTI ID:
- 206400
- Report Number(s):
- ANL/CMB/SUMM-86337; CONF-9508202-07; ON: DE96005234
- Resource Relation:
- Conference: 10. international photosynthesis congress, Montpellier (France), 20-25 Aug 1995; Other Information: PBD: [1995]
- Country of Publication:
- United States
- Language:
- English
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In bacterial reaction centers rapid delivery of the second proton to Q{sub B} can be achieved in the absence of L212Glu.