A cDNA clone encoding a photosystem I protein with homology to photosystem II chlorophyll a/b-binding polypeptides.

Abstract

We report here the isolation and nucleotide sequence of a complete cDNA clone encoding a photosystem I (PS I) polypeptide that is recognized by a monoclonal antibody made against photosystem II (PS II) chlorophyll a/b-binding (CAB) proteins. The deduced sequence of this PS I protein shows 30% overall identity to PS II CAB sequences, and two long segments within this protein show 50% and 65% identity to the corresponding segments in the PS I CAB polypeptides. Even though the sequence of this PS I CAB protein is substantially divergent from PS II CAB sequences, their hydropathy plots are very similar and suggest they all traverse the thylakoid membrane three times. A segment of the PS I CAB polypeptide shows similarity to the functionally analogous (3 subunits of the antenna proteins of purple bacteria. In contrast, no homology was observed between these bacterial proteins and PS II CAB polypeptides. MATERIALS AND METHODSFractionation of PS I and PS 11. Tomato (Lycopersicon esculentum) PS I and PS II were fractionated according to Mullet et al. (14) with the exception that the Triton X-100 concentration was changed to 0,5% (wt/vol) for the solubilization of the thylakoid membrane. Under these conditions, the chlorophyll concentration was 0.8 mg/ml.Polyacrylamide Gel Electrophoresis. Protein samples were subjected to NaDodSO4/polyacrylamide gel electrophoresis in 13% gels under reducing conditions (13,15 Immunoblots. Protein was transferred to nitrocellulose paper at pH 8.3 by applying a voltage gradient of 30 V/cm for 1 hr (17). Transfer was-followed by a 30-min incubation in Tris-buffered saline (TBS; 10 mM Tris HCI, pH 7.5/150 mM NaCl) containing 2% (wt/vol) nonfat dry milk powder. Blots were incubated with antibodies for 16 hr at 40C and washed successively with TBS, TBS containing 0.1% Nonidet P-40, and TBS. Blots incubated with monoclonal antibodies were further incubated with goat anti-mouse immunoglobulin conjugated to alkaline phosphatase as described by Darr et al. (13)

Dicyclohexylcarbodiimide‐binding proteins related to the short circuit of the proton‐pumping activity of photosystem II

“…The fragment obtained from cleavage of the 22-kDa protein (pea) was highly similar (16 out of 18 residues) to the photosystem I type I LHC proteins (tomato) encoded by the CAB6A or AB6B genes (Pichersky et al, 1987b;Hoffman et al, 1987).…”

A cDNA clone encoding a 10.8 kDa photosystem I polypeptide of barley

“…The hydrophobic thylakoid transfer domain shared by these four lumen polypeptides is lacking in the 10.8 kDa polypeptide. Shorter transit peptides comparable to that of the 10.8 kDa polypeptide have been observed for typical intrinsic polypeptides, such as the chlorophyll a/bbinding polypeptides [35,36] and for some stroma localized polypeptides, such as ferredoxin [37]. The properties of the transit peptide of the 10.8 kDa polypeptide show similarities with those of fer- redoxin [38], suggesting a routing of the 10.8 kDa mature polypeptide to the stromal side of the thylakoid membrane.…”

Amino‐terminal sequence of the 21 kDa apoprotein of a minor light‐ harvesting pigment‐protein complex of the Photosystem II antenna (LHC IId/CP24)

“…The LHCI-15 gene also codes for a mature protein that is putatively 13 amino acids longer at the Nterminus than the LHC IId apoprotein. Similarly, Cab-6A, another putative LHC I cDNA clone from tomato coding for a polypeptide of about 24 kDa [22], contains similar regions of homology, although overall it does not appear to be homologous to either LHC IId or LHCI-15 (Fig. 2).…”