An evolutionary conserved Hexim1 peptide binds to the Cdk9 catalytic site to inhibit P-TEFb

作者：Kobbi Lydia; Demey Thomas Emmanuelle; Braye Floriane; Proux Florence; Kolesnikova Olga; Vinh Joelle; Poterszman Arnaud; Bensaude Olivier^*

来源：Proceedings of the National Academy of Sciences, 2016, 113(45): 12721-12726.

DOI：10.1073/pnas.1612331113

• cyclin-dependent kinase inhibition
• transcription factor regulation
• regulatory noncoding RNA
• benzoyl phenylalanine
• protein-protein cross-linking

The positive transcription elongation factor (P-TEFb) is required for the transcription of most genes by RNA polymerase II. Hexim proteins associated with 7SK RNA bind to P-TEFb and reversibly inhibit its activity. P-TEFb comprises the Cdk9 cyclin-dependent kinase and a cyclin T. Hexim proteins have been shown to bind the cyclin T subunit of P-TEFb. How this binding leads to inhibition of the kinase activity of Cdk9 has remained elusive, however. Using a photoreactive amino acid incorporated into proteins, we show that in live cells, cell extracts, and in vitro reconstituted complexes, Hexim1 cross-links and thus contacts Cdk9. Notably, replacement of a phenylalanine, F208, belonging to an evolutionary conserved Hexim1 peptide ((202)PYNTTQFLM(210)) known as the "PYNT" sequence, cross-links a peptide within the activation segment that controls access to the Cdk9 catalytic cleft. Reciprocally, Hexim1 is cross-linked by a photoreactive amino acid replacing Cdk9 W193, a tryptophan within this activation segment. These findings provide evidence of a direct interaction between Cdk9 and its inhibitor, Hexim1. Based on similarities with Cdk2 3D structure, the Cdk9 peptide cross-linked by Hexim1 corresponds to the substrate binding-site. Accordingly, the Hexim1 PYNT sequence is proposed to interfere with substrate binding to Cdk9 and thereby to inhibit its kinase activity.

• 出版日期2016-11-8