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XVI.A.1.d. PSI-I
Sequences of PSI-I
Sequence Similarity Search for PSI-I
XVI.A.1.i. PSI-I
The psaI encodes a polypeptide of about 36 amio acids, and a deduced molecular mass of 4008 Da (for a review see Andersen and Scheller, 1993). The polypeptide is not post-translationally processed except for the possible conversion of a methionine residue into a methionine sulfone.
PSI-I is very hydrophobic. The hydropathy plot indicates the presence of one central embrane-spanning alpha-helix, flanked by hydrophilic N and C termini. It is tightly bound the PSI-A, PSI-B heterodimer. Treatment of isolated PSI-I with chaotropes dissociates many of the smaller polypeptides, but not PSI-I from the heterodimer.
The PSI-I poplypeptide exhibits sequence similarity with helix E of the D2 reaction center polypeptide of PSII. Eleven reidues are identical and 11 non-identical residues represent conservative substitutions. Since helix E participates in the binding of nonheme ironand the quinones of PSII, this raises the possibility that PSI-I may participate in the binding of some of the primary electron acceptors of PSI.
A query for psaI addressed to the various protein databases listed in the Biology Workbench, yielded 60 records which are depicted under Sequenced PSI-I. 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, pub/Antheprot/Windows/anthe 3_1 directory). For example a Blast Sequence Similarity Search of sbarley PSI-I addressed to the Biology Workbench (SwissProt database) is depicted below.
Sequences of PSI-I
Click on Sequences to view the sequences of PSI-I retrieved from various protein sequence databases by the Biology Workbench.
Sequence Similarity Search for PSI-I
Click on Sequence Similarity Search to view the Blast sequence similarity search results of barley PSI-I 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.