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Author Notes:

Correspondence to: John M. Nickerson, PhD, Room B5602, Emory Eye Center, Emory University, 1365B Clifton Road, N.E., Atlanta, GA, 30322; Phone: (404) 778-4411; FAX: (404) 778-2231; email: litjn@emory.edu

Dr. Gross is now at the Picower Institute for Medical Research, 350 Community Drive, Manhasset, NY, 11030


Research Funding:

These studies were funded by NIH R01 EY10553 (to JMN), P30 EY06360, and T32 EY 07092; a Center grant from the Foundation Fighting Blindness; and an unrestricted grant to the Emory Eye Center from Research to Prevent Blindness; and the Director, Office of Science, Office of Basic Energy Sciences, U.S. Department of Energy, under Contract number DE-AC03-76SF0098 (to ISM).

Prediction of structural and functional relationships of Repeat 1 of human interphotoreceptor retinoid-binding protein (IRBP) with other proteins


Journal Title:

Molecular Vision


Volume 2000, Number 6


, Pages 30-39

Type of Work:

Article | Final Publisher PDF


Purpose: We compared the structure and function of interphotoreceptor retinoid-binding protein (IRBP) related proteins and predicted domain and secondary structure within each repeat of IRBP and its relatives. We tested whether tail specific protease (Tsp), which bears sequence similarity to IRBP Domain B, binds fatty acids or retinoids, and whether IRBP possessed protease activity resembling Tsp's catalytic function. These tests helped us to learn whether the primary sequence similarities of family members extended to higher order structural and functional levels. Methods: Predictions derived from multiple sequence alignments among IRBP and Tsp family members and secondary structure computer programs were carried out. The first repeat of human IRBP (EcR1) and Tsp were expressed, purified, and tested for binding properties. Tsp was examined for fluorescence enhancement of retinol or 16-anthroyloxy-palmitic acid (16-AP) to test for ligand binding. IRBP was tested for protease activity. Results: Tsp did not exhibit fluorescence enhancement with retinol or 16-AP. IRBP did not exhibit protease activity. The positions of critical residues needed for the ligand binding properties of retinol were predicted. Primary sequence and three-dimensional similarity was found between Domain A of IRBP Repeat 3 and eglin c. Conclusions: The sequence similarity of Tsp and IRBP raised the possibility that each might share the function of the other protein: IRBP might possess protease activity or Tsp might possess retinoid or fatty acid binding activity. Our studies do not support such a shared function hypothesis, and suggest that the sequence similarity is the result of maintenance of structure. The finding of similarity to eglin c in Domain A suggests the possibility of a tight interaction between Domain A and Domain B, possibly implying the need for Domain A in retinoid-binding, and suggesting that both Domains should be present in testing mutations. The positions of predicted critical amino acids suggest models in which a large binding pocket holds the retinoid or fatty acid ligand. These predictions are tested in a companion paper.

Copyright information:

© 2000 Molecular Vision

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