Defining unique structural features in the MAFA and MAFB transcription factors that control Insulin gene activity.

MAFA and MAFB are related basic-leucine-zipper domain-containing transcription factors which have important overlapping and distinct regulatory roles in a variety of cellular contexts, including hormone production in pancreatic islet cells. Here, we first examined how mutating conserved MAF protein-DNA contact sites obtained from X-ray crystal structure analysis impacted their DNA-binding and Insulin enhancer-driven activity. While most of these interactions were essential and their disruption severely compromised activity, we identified that regions outside of these contact sites also contributed to transcriptional activity. AlphaFold 2 (https://alphafold.ebi.ac.uk), an artificial intelligence-based structural prediction program, was used to determine if there were also differences in the three-dimensional organization of the non-DNA binding/dimerization sequences of MAFA and MAFB. This analysis was conducted on the WT proteins as well as the pathogenic MAFA(Ser64Phe) and MAFB(Ser70Ala) transactivation domain mutants, with differences revealed between MAFA(WT) and MAFB(WT) as well as between MAFA(Ser64Phe) and MAFA(WT), but not between MAFB(Ser70Ala) and MAFB(WT). Moreover, dissimilarities between these proteins were also observed in their ability to cooperatively stimulate Insulin enhancer-driven activity in the presence of other islet-enriched transcription factors. Analysis of MAFA and MAFB chimeras disclosed that these properties were influenced by their unique C-terminal region structural differences predicted by AlphaFold 2. Our findings have revealed key structural features of these closely related proteins that impact their ability to regulate gene expression.