Acta Crystallographica Section D

Biological Crystallography

Volume 69, Part 8 (August 2013)

research papers

Acta Cryst. (2013). D69, 1598-1608    [ doi:10.1107/S0907444913011360 ]

The structure of full-length human CTNNBL1 reveals a distinct member of the armadillo-repeat protein family

X. Huang, G. Wang, Y. Wu and Z. Du

Abstract: Catenin-[beta]-like protein 1 (CTNNBL1) is a highly conserved protein with multiple functions, one of which is to act as an interaction partner of the antibody-diversification enzyme activation-induced cytidine deaminase (AID) for its nuclear import and subnuclear trafficking. Here, the crystal structure of full-length human CTNNBL1 is reported. The protein contains six armadillo (ARM) repeats that pack into a superhelical ARM domain. This ARM domain is unique within the ARM protein family owing to the presence of several unusual structural features. Moreover, CTNNBL1 contains significant and novel non-ARM structures flanking both ends of the central ARM domain. A strong continuous hydrophobic core runs through the whole structure, indicating that the ARM and non-ARM structures fold together to form an integral structure. This structure defines a highly restrictive and discriminatory protein-binding groove that is not observed in other ARM proteins. The presence of a cluster of histidine residues in the groove implies a pH-sensitive histidine-mediated mechanism that may regulate protein binding activity. The many unique structural features of CTNNBL1 establish it as a distinct member of the ARM protein family. The structure provides critical insights into the molecular interactions between CTNNBL1 and its protein partners, especially AID.

PDB references: 4hm9 and 4hnm

Keywords: armadillo repeat; CTNNBL1; AID; nuclear import.

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[ doi:10.1107/S0907444913011360/mn5029sup1.pdf ]
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