title: Cyt c6-3: A New Isoform of Photosynthetic Cyt c6 Exclusive to Heterocyst-Forming Cyanobacteria.
abstract: All known cyanobacteria contain Cyt c6, a small soluble electron carrier protein whose main function is to transfer electrons from the Cyt b6f complex to PSI, although it is also involved in respiration. We have previously described a second isoform of this protein, the Cyt c6-like, whose function remains unknown. Here we describe a third isoform of Cyt c6 (here called Cytc6-3), which is only found in heterocyst-forming filamentous cyanobacteria. Cyt c6-3 is expressed in vegetative cells but is specifically repressed in heterocysts cells under diazotrophic growth conditions. Although there is a close structural similarity between Cyt c6-3 and Cyt c6 related to the general protein folding, Cyt c6-3 presents differential electrostatic surface features as compared with Cyt c6, its expression is not copper dependent and has a low reactivity towards PSI. According to the different expression pattern, functional reactivity and structural properties, Cyt c6-3 has to play an as yet to be defined regulatory role related to heterocyst differentiation.
authors.affiliation: School of Medicine, Department of Anatomy and Neurobiology, Medical Science Campus of the University of Puerto Rico (MCS-UPR), San Juan, PR, USA.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Torrado
authors.affiliation: Department of Environmental, Earth and Geospatial Sciences, North Carolina Central University, Durham, North Carolina, USA.
authors.forename: Ana
authors.initials: A
authors.lastname: Valladares
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla-CSIC, Avda Américo Vespucio, Sevilla, Spain.
authors.forename: Leonor
authors.initials: L
authors.lastname: Puerto-Galán
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla and Consejo Superior de Investigaciones Científicas Seville, Spain.
authors.forename: Manuel
authors.initials: M
authors.lastname: Hervás
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla and Consejo Superior de Investigaciones Científicas Seville, Spain.
authors.forename: José A
authors.initials: JA
authors.lastname: Navarro
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla-CSIC, Avda Américo Vespucio, Sevilla, Spain.
authors.forename: Fernando P
authors.initials: FP
authors.lastname: Molina-Heredia
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D000458:Cyanobacteria / Q000378:metabolism*; D004579:Electron Transport / Q000502:physiology; D010788:Photosynthesis / Q000502:physiology; D010970:Plastocyanin / Q000378:metabolism; D020033:Protein Isoforms / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D020033:Protein Isoforms; D010970:Plastocyanin
keywords: Cyanobacteria; Cyt c6; Cyt c6-3; Cyt c6-like; Heterocysts; Nostoc sp. PCC 7119; PSI; Photosynthetic electron transfer chain; Plastocyanin; Respiratory electron transfer chain