Untersuchungen zur Funktion von Alb 3 im plastidären Proteintransport von Arabidopsis thaliana
Members of the Oxa1 protein family mediate the integration of proteins in their respective membranes. To the date, homologs within mitochondria (Oxa1p), E. coli (YidC) and chloroplasts (Alb3) have been investigated. Alb3 is the least investigated protein of this triple. A function within thylakoid membrane biogenesis is discussed for Alb3, but the only known substrates so far are proteins of the LHCP family. Nothing is known about the mechanism by which these substrates are integrated into the thylakoid membrane, nore about the exact function of Alb3 in this process. Therefore, the role of Alb3 in protein transport has been investigated more closely. Gel permeation chromatography (GPC) experiments have shown that Alb3 is part of a high molecular protein complex. The size of this complex is dependent on the detergent used and varies about 160-200 kD. CpSecY co-fracctionates with these complexes. A range of protein complexes (160-700 kD) containing Alb3 and cpSecY have been observed in blue native gel analysis, with the main fraction residing at about 160 kD, correlating with the GPC data. Both proteins are associated within the same complex, as has been demonstrated by precipitation experiments: cpSecY was co-precipitated by antibodies raised against Alb3 and vice versa. The association within the same complex is further corroborated by the fact that crosslinking of thylakoid membranes with the homobifunctonal, aminoreactive crosslinker DSS gave raise to crosslinking products in the size about 90 kD, containing both Alb3 and cpSecY. The second part of the work is concerned with the ALB3 homolog HOM3 which codes a putative chloroplast protein. The cDNA has been cloned and precursor protein synthesized by in vitro transcription and translation. The precursor protein imported into intact chloroplasts thus confirming the chloroplast localization. Lysis of the chloroplasts showed, that Hom3 is localized within the membrane fraction.
info:eu-repo/classification/ddc/580, Ackerschmalwand, Chloroplast, Thylakoidmembran, Proteintransport, Pflanzen (Botanik), Oxa1-Familie, Sec-Translokase
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