KDM subfamily 6 enzymes KDM6A and KDM6B specifically catalyse demethylation of di-/tri-methylated lysine on Histone 3 lysine 27 (H3K27me3/2) and play an important role in repression of developmental genes. Despite identical amino acid sequence in the immediate surroundings of H3K9me3/2 (ARKS) the enzymes do not catalyse demethylation of this general marker of repression. In order to address this question for KDM6B we used computational methods to identify H3(17-33) derived peptides with improved binding affinity, that would enable co-crystallization with the catalytic core of human KDM6B (ccKDM6B). A total of five peptides were identified and their IC50 values were determined in a MALDI-TOF based assay. Despite... More
KDM subfamily 6 enzymes KDM6A and KDM6B specifically catalyse demethylation of di-/tri-methylated lysine on Histone 3 lysine 27 (H3K27me3/2) and play an important role in repression of developmental genes. Despite identical amino acid sequence in the immediate surroundings of H3K9me3/2 (ARKS) the enzymes do not catalyse demethylation of this general marker of repression. In order to address this question for KDM6B we used computational methods to identify H3(17-33) derived peptides with improved binding affinity, that would enable co-crystallization with the catalytic core of human KDM6B (ccKDM6B). A total of five peptides were identified and their IC50 values were determined in a MALDI-TOF based assay. Despite none of the peptides showing showed significantly higher affinity compared to the H3(17-33) peptide, it was possible to co-crystallize ccKDM6B with a H3(17-33)A21M peptide. This structure reveals the interactions between the KDM6B zinc binding domain and the H3(17-23) region. Although KDM6A and KDM6B differ in primary sequence, particularly in the H3L20 binding pocket of the zinc binding domains, where to histidines in KDM6A have been replaced by a glutamate and a tyrosine, they bind the H3(17-23) in a very similar fashion. This structure shows that KDM6B, in analogy with KDM6A, also uses the zinc binding domain to achieve H3K27me3/me2 specificity. The histidine to glutamine substitution at amino acid position 1564 in the KDM6B zinc binding domain can further rationalize, why KDM6B binds substrates with higher affinity than KDM6A.
