A stresszfehérjék és lipidek membrán kapcsolt homeosztázisa = Coupled homeostasis of membrane lipids and stress proteins

1. Megallapitottuk, hogy az IbpA/B feherje in vivo kulonboző mertekben asszocialodik az E. coli membran(ok)hoz. Langmuir-Blodget monolayer kiserletekben igazoltuk az IbpAB membranlipid koteset. Jellemeztuk az E. coli IbpAB- mutanst mind molekularis, mind fiziologias szinten. Megallapitottuk, hogy az IbpAB- mutans torzsek rendelkeznek „membran-fenotipussal”, a vad tipustol markansan elterő lipid zsirsavosszetetellel, valamint megvaltozott fluiditassal es permeabilitassal. A lipidomikai kiserletek ravilagitottak a fluiditasvaltozas kompenzacios jellegere, a homeosztatikus membran adaptacio elvenek megfelelően. A membranlipidek es hősokkfeherjek kapcsolatanak egy masik dimenziojara kivantunk ravilagitani a vad tipusu es mutans torzsek globalis „transcriptome” analizisevel. A wt es az IbpAB mutansok mRNS profilja hatalmas elterest mutat, a valtozasok genek egesz sorat erintik, amelyek megertese tovabbi kiserleteket kivan. 2. Munkank soran elsőkent igazoltuk Synechocystisben a DnaK2 feherje szubfrakciojanak tilakoid asszociaciojat. A DnaK2 reszleges hianya megvaltoztatta a tilakoid membran lipid- es zsirsavosszetetelet, valamint a membran fizikai allapotat. A membranvaltozasok befolyasoljak a tilakoid membran műkodeset, ami elterő hő- illetve UV-B stresszerzekenysegben is megnyilvanul. A DnaK2 protein reszleges hianya UV karosodas utan a PSII “repair” reszleges inhibiciojat eredmenyezte. Ily modon kimutattuk egy uj, membranasszocialt DnaK-fuggő stresszvedő mechanizmus letezeset. | 1. In E. Coli the small heat shock protein IbpAB interacts with membranes in vivo and in vitro and rigidifides it which counterbalances heat-induced fluidization, indicating a protective role of this Hsp in the heat-shocked membrane. IbpAB- cells have an increased membrane permeability but higher outer membrane transition temperature and better survival at heat challenge. The improved survival is linked to the altered membrane phenotype. These include unique fatty acid changes and fluidization in the hydrophobic core of the membranes, which are associated with better survival upon heat challenge. 2. We have shown that in Synechocystis PCC6803 DnaK2 chaperon interacts with the thylakoid membrane, especially with the phosphatidyl glycerol (PG) lipid of the thylakoid. In DnaK2- cells the fatty acid composition of the thylakoid membrane differed from that of the wild type resulting in altered physico-chemical properties. We exposed cells to UV-B damage and concluded, that lack of the DnaK2 leads to partial inhibition of PSII repair and the rate of forward electron transport between QA and QB quinone electron acceptors is slowed down. PG plays an important role in binding extrinsic proteins required for a functional Mn cluster on the donor side of PSII. The binding of DnaK2 may take place trough binding specifically to PG and/or with the PSII complex. This interaction leads directly or indirectly to change in membrane fluidity which influences PSII electron transport.