Tic22 from Anabaena sp. PCC 7120 with holdase function involved in outer membrane protein biogenesis shuttles between plasma membrane and Omp85

Abstract

β-barrel-shaped outer membrane proteins (OMPs) ensure regulated exchange of molecules across the cell-wall of Gram-negative bacteria. They are synthesized in the cytoplasm and translocated across the plasma membrane via the SEC translocon. In the periplasm, several proteins participate in the transfer of OMPs to the outer membrane-localized complex catalyzing their insertion. This process has been described in detail for proteobacteria and some molecular components are conserved in cyanobacteria. For example, Omp85 proteins that catalyze the insertion of OMPs into the outer membrane exist in cyanobacteria as well. In turn, SurA and Skp involved in OMP transfer from plasma membrane to Omp85 in E. coli are likely replaced by Tic22 in cyanobacteria. We describe that anaTic22 functions as periplasmic holdase for OMPs in Anabaena sp. PCC 7120 and provide evidence for the process of substrate delivery to ana Omp85. Ana Tic22 binds to the plasma membrane with specificity for phosphatidylglycerol and monogalactosyldiacylglycerol. Substrate recognition induces membrane dissociation and interaction with the N-terminal POTRA domain of Omp85. This leads to substrate release by the interaction with a proline-rich domain and the first POTRA domain of Omp85. The order of events during OMP transfer from plasma membrane to Omp85 in cyanobacteria is discussed. Abbreviations: BAM, β-barrel assembly machinery; DGDG, digalactosyldiacylglycerol; MGDG, monogalactosyldiacylglycerol; OM, outer membrane; OMP, OM proteins; PC, phosphatidylcholine; PG, phosphatidylglycerol; PGL, peptidoglycan layer; PM, plasma membrane; POTRA, polypeptide-transportassociated domains; SQDG, sulfoquinovosyldiacylglycerol; TIC, translocon of the inner envelope membrane of chloroplasts.

Comparative Phenotypic Analysis of Anabaena sp. PCC 7120 Mutants of Porinlike Genes

“…The upper band corresponds to the full length protein, whereas the lower molecular weight signal most likely represents a degradation product. Both fragments have been detected in wild type in previous experiments [45].…”

“…2B, first and second panel). This behavior was not described before [45,46,59] as the effect was only visible when the culture was sufficiently diluted (Fig. 2B, second panel).…”

Evidence Supporting an Antimicrobial Origin of Targeting Peptides to Endosymbiotic Organelles

“…In contrast, the eukaryotic ancestor of Archeplastidia was in some way “pre-adapted” for the recruitment of Class I HA-RAMP for import functions. This does not mean that cTPs merely have recruited the TOM/TIM that form the protein channel as well as Tic21, Tic22, Tic23, Tic32, Tic55 and Tic62 are of cyanobacterial origin [ 97 , 98 , 99 ]. However, we anticipate a common origin of some TIC and TIM subunits which will require an extensive phylogenetic analysis of the two sets of translocon components.…”

Cyclophilin anaCyp40 regulates photosystem assembly and phycobilisome association in a cyanobacterium

“…4d ) and the color of the fraction (not shown). To distinguish between an interaction with PBS and a co-migration of ana Cyp40 in this fraction, PBS total lysate was isolated from AFS- anacyp40 -strep, and probed with antibodies against the strep tagged protein or the periplasmic localized ana Tic22 55 . While both proteins were detected in the cell lysate (Fig.…”

“…In total, 4 SCX fractions were collected by eluting first 3 fractions in 75, 200, 400 NH 4 HCO 3 /30% ACN/0.5% TFA solutions followed by a final elution with 5% mM ammonium hydroxide/50% ACN. Fractions eluted were dried in a SpeedVac, resuspended in ddH 2 O and subjected to LC-MS analysis as described 55 .…”