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Structural basis for tunable affinity and specificity of LxCxE-dependent protein interactions with the retinoblastoma protein family.

ABSTRACT: The retinoblastoma protein (Rb) and its homologs p107 and p130 are critical regulators of gene expression during the cell cycle and are commonly inactivated in cancer. Rb proteins use their "pocket domain" to bind an LxCxE sequence motif in other proteins, many of which function with Rb proteins to co-regulate transcription. Here, we present binding data and crystal structures of the p107 pocket domain in complex with LxCxE peptides from the transcriptional co-repressor proteins HDAC1, ARID4A, and EID1. Our results explain why Rb and p107 have weaker affinity for cellular LxCxE proteins compared with the E7 protein from human papillomavirus, which has been used as the primary model for understanding LxCxE motif interactions. Our structural and mutagenesis data also identify and explain differences in Rb and p107 affinities for some LxCxE-containing sequences. Our study provides new insights into how Rb proteins bind their cell partners with varying affinity and specificity.

SUBMITTER: Putta S

PROVIDER: S-EPMC9444907 | biostudies-literature | 2022 Sep

REPOSITORIES: biostudies-literature

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Structural basis for tunable affinity and specificity of LxCxE-dependent protein interactions with the retinoblastoma protein family.

Putta Sivasankar S Alvarez Lucia L Lüdtke Stephan S Sehr Peter P Müller Gerd A GA Fernandez Samantha M SM Tripathi Sarvind S Lewis Joe J Gibson Toby J TJ Chemes Lucia B LB Rubin Seth M SM

Structure (London, England : 1993) 20220617 9

The retinoblastoma protein (Rb) and its homologs p107 and p130 are critical regulators of gene expression during the cell cycle and are commonly inactivated in cancer. Rb proteins use their "pocket domain" to bind an LxCxE sequence motif in other proteins, many of which function with Rb proteins to co-regulate transcription. Here, we present binding data and crystal structures of the p107 pocket domain in complex with LxCxE peptides from the transcriptional co-repressor proteins HDAC1, ARID4A, a ...[more]

PMID: 35716663

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Project description:BackgroundProtein Kinase Casein Kinase 2 (PKCK2) is an ubiquitous Ser/Thr kinase expressed in all eukaryotes. It phosphorylates a number of proteins involved in various cellular processes. PKCK2 holoenzyme is catalytically active tetramer, composed of two homologous or identical and constitutively active catalytic (alpha) and two identical regulatory (beta) subunits. The tetramer cannot phosphorylate some substrates that can be phosphorylated by PKCK2alpha in isolation. The present work explores the structural basis of this feature using computational analysis and modeling.ResultsWe have initially built a model of PKCK2alpha bound to a substrate peptide with a conformation identical to that of the substrates in the available crystal structures of other kinases complexed with the substrates/ pseudosubstrates. In this model however, the fourth acidic residue in the consensus pattern of the substrate, S/T-X-X-D/E where S/T is the phosphorylation site, did not result in interaction with the active form of PKCK2alpha and is highly solvent exposed. Interaction of the acidic residue is observed if the substrate peptide adopts conformations as seen in beta turn, alpha helix, or 3(10) helices. This type of conformation is observed and accommodated well by PKCK2alpha in calmodulin where the phosphorylation site is at the central helix. PP2A carries sequence patterns for PKCK2alpha phosphorylation. While the possibility of PP2A being phosphorylated by PKCK2 has been raised in the literature we use the model of PP2A to generate a model of PP2A-PKCK2alpha complex. PKCK2beta undergoes phosphorylation by holoenzyme at the N-terminal region, and is accommodated very well in the limited space available at the substrate-binding site of the holoenzyme while the space is insufficient to accommodate the binding of PP2A or calmodulin in the holoenzyme.ConclusionCharge and shape complimentarity seems to play a role in substrate recognition and binding to PKCK2alpha, along with the consensus pattern. The detailed conformation of the substrate peptide binding to PKCK2 differs from the conformation of the substrate/pseudo substrate peptide that is bound to other kinases in the crystal structures reported. The ability of holoenzyme to phosphorylate substrate proteins seems to depend on the accessibility of the P-site in limited space available in holoenzyme.

Dataset Information

Structural basis for tunable affinity and specificity of LxCxE-dependent protein interactions with the retinoblastoma protein family.

Publications

Structural basis for tunable affinity and specificity of LxCxE-dependent protein interactions with the retinoblastoma protein family.

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