=============================================================================
Click on a topic to go directly to it.
XVI.A.1.c. PSI-C
Sequences of PSI-C
Sequence Similarity Search for PSI-C
XVI.A.1.c. PSI-C
PSI-C is a 9-kDa polypeptide that carries the electron acceptors A and B (for a review see Andersen and Scheller, 1993). It is encoded by the chloroplast psaC gene. The amino acid sequence of PSI-C (see sequences) is highly conserved among species and shows a pattern of cysteine residues that is characteristic of 2[4Fe-4S] proteins. Alignment analysis reveals a primary amino acid structure similar to the structure of soluble bacterial ferredoxins of the 2[4Fe-4S] type. In addition however, PSI-C contains 14 additional amino acids at the C-terminal and an insert of 8 amino acids in the middle of the polypeptide. While the extended C-terminus is hydrophilic, the inserts show a higher degree of hydrophobicity. Since PSI-C is membrane-bound, the additional amino acids in the insert may be responsible for the binding of PSI-C to the PSI complex.
PSI-C is rather hydrophilic and exhibits no membrane-spanning segments. Since electron transfer in PSI proceeds directly from the B and A centers to soluble ferredoxin in the stroma, this implies a peripheral location of PSI-C on the stromal side of the thylakoid membrane. Furthermore, PSI-C is very resistant to protease treatment of isolated thylakoid membranes. Since PSI-D and PSI-E appear to be closely located near PSI-C, it has been suggested that they shelter the latter from the action of proteases.
A query for psaC addressed to the Various protein databases listed in the Biology Workbench, yielded 64 records which are depicted under Sequenced PSI-C. These sequences can be used for Sequence Similarity Searches or other manipulations using one of several routines described in the Biology Workbench or elsewhere (see AntheproW which can be downloaded via anonymous ftp from: ibcp.fr, in the pub/Antheprot/Windows/anthe 3_1 directory). For example a Blast Sequence Similarity Search of spinach PSI-B addressed to the Biology Workbench (SwissProt database) is depicted below.
Sequences of PSI-C
Click on Sequences to view the sequences of PSI-C retrieved from various protein sequence databases by the Biology Workbench.
Sequence Similarity Search for PSI-C
Click on Sequence Similarity Search to view the Blast sequence similarity search results of spinach PSI-C from the Biology workbench (SwissProt database).
References
- Andersen, B. and H. V. Scheller (1993). Structure, Function and Assembly of photosystem I. In: Pigment-Protein Complexes In Plastids: Synthesis and Assembly . C. Sundqvist and M. Ryberg, (eds.), p 383-417, Academic Press, New York.