Vitamin A Research Today is a free monthly online journal that collates and summarizes the latest research about Vitamin A, including details on retinol, benefits, dosage, supplements, deficiency, information.

Location and functional significance of retinol-binding sites on the serine/threonine kinase, c-Raf.

Hoyos B, Jiang S, Hammerling U

Immunology Program, Memorial Sloan Kettering Cancer, New York, New York, 10021, USA. b-hoyos@ski.mskcc.org

Redox activations of serine/threonine kinases represent alternate pathways in which vitamin A plays a crucial co-factor role. Vitamin A binds the zinc finger domain of c-Raf with nanomolar affinity. The retinoid-binding site has been mapped within this structure by scanning mutagenesis. The deduced contact sites were found anchored on Phe-8, counting from the 1st conserved histidine of the zinc finger. These sites agreed with contact amino acids identified by computational docking. The boundaries of a related binding pocket were identified by mutagenesis and partially confirmed by docking trials in the protein kinase C-alpha C1A zinc finger. They comprised Phe-7, Phe-8, and Trp-22. This trio was absent from the alphaC1B domain, explaining why the latter did not bind retinol. Reconfiguring at a minimum the two corresponding amino acids of alphaC1B, Thr-7 and Tyr-22, to conform to alphaC1A converted this domain to a binder. Deletion of the predicted retinoid-binding site in the full-length molecule created a mutant c-Raf that was deficient in retinol-dependent redox activation but fully responsive to epidermal growth factor. Our findings indicate that ligation of retinol to a specific site embedded in the regulatory domain is an important feature of c-Raf regulation in the redox pathway.

Published 21 February 2005 in J Biol Chem, 280(8): 6872-8.
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