An amino-proximal hydrophobic domain in the major light-harvesting chlorophyll a/b-protein is essential for membrane integration and protein stability

The major light-harvesting chlorophyll a/b-protein (LHCP) of higher plant chloroplasts is a nuclearencoded, integral thylakoid membrane protein that binds photosynthetic pigments and occurs in situ in an oligomeric form. We have previously examined structural and functional domains of the mature apoprotein by use of mutant LHCPs and in vitro assays for uptake and insertion. Results presented here demonstrate the effects of several mutations in the amino terminal domain of the mature apoprotein. Deletion of amino acid residues 12–58 greatly affected import into chloroplasts, while deletion or alteration of the hydrophobic region E⁶⁵VIHARWAM⁷³ led to rapid degradation of the mutant LHCP. We suggest that this amino-proximal region is essential for the stability of the LHCP and its ability to integrate into the thylakoid membranes. A structural/functional relationship of this region to a previously examined hydrophobic carboxy-proximal domain [Kohorn and Tobin (1989), The Plant Cell 1, 159–166] is proposed.Abbreviations BSA bovine serum albumin faction V - ELIPs early light-inducible proteins - Hepes 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - LHCP light-harvesting chlorophyll a/b-protein - LHC IIb light-harvesting complex associated with Photosystem II - pLHCP precursor to LHCP - Rubisco ribulose 1,5-biphosphate carboxylase-oxygenase - SDS-PAGE sodium dodecyl sulfate-poly-acrylamide gel electrophoresis