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replacement of the entire beta1-beta3 region, Ile250 to Ile283, of the cyaB1 GAF B subdomain with Asn411 to Tyr443 of GAF B from rat phosphodiesterase 2, is stimulated by cGMP 10.5fold similar to wild-type cyaB1, whereas activation by cAMP is eliminated, thus switched specificity of the cyaB1 tandem GAF domain from cAMP to cGMP. Swapping of the anterior part, Ile250 to Gly267, in cyaB1 GAF B with Asn411 to Asn426 of rat phosphodiesterase 2, which is stimulated by neither cAMP nor cGMP up to 10 mM. Swapping the C-terminal W270 to I283 section of cyaB1 for Val429 to Tyr443 from rat phosphodiesterase 2 yields a protein that is highly stimulated by both cAMP and cGMP, i.e. purine specificity is lost. Elongation of the swapped stretch of amino acids towards the N-terminal, e.g. when Thr258/Leu259 are included in the domain swapping and replaced by Ser and Val cNMP, specificity is inverted, i.e. the efficacy of cAMP is almost lost, whereas cGMP stimulates cyaB1 AC potently |
Anabaena sp. |