A mutation in the cofactor-binding domain of 11 beta-hydroxysteroid dehydrogenase type 2 associated with mineralocorticoid hypertensions

Renal 11 beta -hydroxysteroid dehydrogenase type 2 (11 beta HSD2) is an enz yme responsible for the peripheral inactivation of cortisol to cortisone in mineralocorticoid target tissues. Mutations in the gene encoding 11 beta H SD2 cause the syndrome of apparent mineralocorticoid excess (AME), an autos omal recessive form of inherited hypertension, in which cortisol acts as a potent mineralocorticoid. The mutations reported to date have been confined to exons 3-5. Here, we describe two siblings, 1 and 2 yr old, who were diagnosed with hyp okalemic hypertension and low plasma aldosterone and renin levels, indicati ng mineralocorticoid hypertension. Analysis of urinary steroid metabolites showed a markedly impaired metabolism of cortisol, with (tetrahydrocortisol + 5 alpha -tetrahydrocortisol)/tetrahydrocortisone ratios of 40-60, and ne arly absent urinary free cortisone. Although phenotypically normal, the het erozygous parents showed a disturbed cortisol metabolism. Genetic analysis of the HSD11B2 gene from the AME patients revealed the hom ozygous deletion of six nucleotides in exon 2 with the resultant loss of am ino acids Leu(114) and Glu(115), representing the first alteration found in the cofactor-binding domain. The deletion mutant, expressed in HEK-293 cel ls, showed an approximately 20-fold lower maximum velocity but increased ap parent affinity for cortisol and corticosterone. In contrast, two additiona lly constructed substitutions, Glu(115) to Gln or Lys, showed increased max imal velocity and apparent affinity for 11 beta -hydroxyglucocorticoids. Fu nctional analysis of wild-type and mutant proteins indicated that a disturb ed conformation of the cofactor-binding domain, but not the missing negativ e charge of GlU(115), led to the observed decreased activity of the deletio n mutant. Considered together, these findings provide evidence for a role o f GlU(115) in determining cofactor-binding specificity of 11 beta HSD2 and emphasize the importance of structure-function analysis to elucidate the mo lecular mechanism of AME.