分类： 生物学 >> 生物物理学 提交时间： 2016-05-12
摘要： Ubiquitination is a post-translational modification that is involved in myriad cellar regulation and disease pathways. The ubiquitin-conjugating enzyme (E2) is an important player in the ubiquitin transfer pathway. Although many E2 structures are available, not all E2 families have known structures, and three-dimensional structures from fungal organisms other than yeast are lacking. We report here the crystal structure of UbcA1, which is a novel ubiquitin-conjugating enzyme identified from the edible and medicinal mushroom Agrocybe aegerita and displays potential antitumor properties. The protein belongs to the Ube2w family and shows similar biochemical characteristics to human Ube2w, including monomer-dimer equilibrium in solution, alpha-NH2 ubiquitin-transfer activity and a mechanism to recognize backbone atoms of intrinsically disordered N-termini in substrates. Its structure displays a unique C-terminal conformation with an orientation of helix alpha 3 that is completely different from the reported E2 structures but similar to a recently reported NMR ensemble of Ube2w. A mutagenesis study on this novel enzyme revealed that an intact C-terminus is significant for protein dimerization and enzymatic activity. As the first crystallized full-length protein of this family, UbcA1 may supersede the truncated X-ray structure of Ube2w (PDB entry 2A7L) as the representative structure of the Ube2w family.
分类： 生物学 >> 生物物理学 >> 生物物理、生物化学与分子生物学 提交时间： 2016-05-12
摘要： Tandem-arranged PDZ [PSD-95 (postsynaptic density-95), Dlg (discs large homologue) and ZO-1 (zonula occludens-1)] domains often form structural and functional supramodules with distinct target-binding properties. In the present study, we found that the two PDZ domains within the PDZ34 tandem of Scribble, a cell polarity regulator, tightly pack in a 'front-to-back' mode to form a compact supramodule. Although PDZ4 contains a distorted alpha B/beta B pocket, the attachment of PDZ4 to PDZ3 generates an unexpected interdomain pocket that is adjacent to and integrates with the canonical aB/aB pocket of PDZ3 to form an expanded target-binding groove. The structure of the PDZ34-target peptide complex further demonstrated that the peptide binds to this expanded target-binding groove with its upstream residues anchoring into the interdomain pocket directly. Mutations of the interdomain pocket and disruptions of the PDZ34 supramodule both interfere with its target-binding capacity. Therefore, the interdomain interface between the PDZ34 supramodule is intrinsically required for its target recognition and determines its target-binding specificity. This interdomain interface-mediated specific recognition may represent a novel mode of target recognition and would broaden the target-binding versatility for PDZ supramodules. The supramodular nature and target recognitionmode of the PDZ34 tandem found in the present study would also help to identify the new binding partners of Scribble and thus may direct further research on the PDZ domain-mediated assembly of Scribble polarity complexes.
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