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Articles by Mingjie Zhang
Total Records ( 3 ) for Mingjie Zhang
  Chunying Song , Wenyu Wen , Suresh K. Rayala , Mingzhi Chen , Jianpeng Ma , Mingjie Zhang and Rakesh Kumar
  Dynein light chain 1 (DLC1, also known as DYNLL1, LC8, and PIN), a ubiquitously expressed and highly conserved protein, participates in a variety of essential intracellular events. Transition of DLC1 between dimer and monomer forms might play a crucial role in its function. However, the molecular mechanism(s) that control the transition remain unknown. DLC1 phosphorylation on Ser88 by p21-activated kinase 1 (Pak1), a signaling nodule, promotes mammalian cell survival by regulating its interaction with Bim and the stability of Bim. Here we discovered that phosphorylation of Ser88, which juxtapose each other at the interface of the DLC dimer, disrupts DLC1 dimer formation and consequently impairs its interaction with Bim. Overexpression of a Ser88 phosphorylation-inactive DLC1 mutant in mammary epithelium cells and in a transgenic animal model caused apoptosis and accelerated mammary gland involution, respectively, with increased Bim levels. Structural and biophysical studies suggested that phosphorylation-mimicking mutation leads to dissociation of the DLC1 dimer to a pure folded monomer. The phosphorylation-induced DLC1 monomer is incapable of binding to its substrate Bim. These findings reveal a previously unrecognized regulatory mechanism of DLC1 in which the Ser88 phosphorylation acts as a molecular switch for the transition of DLC1 from dimer to monomer, thereby modulating its interaction with substrates and consequently regulating the functions of DLC1.
  Wei Feng , Hao Wu , Ling-Nga Chan and Mingjie Zhang
  PDZ domain-containing scaffold protein Par-3 is the central organizer of the evolutionarily conserved cell polarity-regulatory Par-3·Par-6·atypical protein kinase C complex. The PDZ domains of Par-3 have also been implicated as potential phosphoinositide signaling integrators, since its second PDZ domain binds to phosphoinositides, and the third PDZ interacts with phosphoinositide phosphatase PTEN. However, the molecular basis of Par-3/PTEN interaction is still poorly understood. Additionally, it is not known whether the regulatory function of PTEN in cell polarity is specifically mediated by its interaction with Par-3. The structures of Par-3 PDZ3 in both its free and PTEN tail peptide-bound forms determined in this work reveal that Par-3 PDZ3 binds to PTEN with two discrete binding sites: a canonical PDZ-ligand interaction site and a distal, opposite charge-charge interaction site. This distinct target recognition mechanism confers the interaction specificity of the Par-3·PTEN complex. We show that the Par-3 PDZ3-PTEN binding is required for the enrichment of PTEN at the junctional membranes of Madin-Darby canine kidney cells. Finally, we demonstrate that the junctional membrane-localized PTEN is specifically required for the polarization of Madin-Darby canine kidney cells. These results, together with earlier data, firmly establish that Par-3 functions as a scaffold in integrating phosphoinositide signaling events during cellular polarization.
  Wenyu Wen , Wei Liu , Jing Yan and Mingjie Zhang
  Rho kinase (ROCK), a downstream effector of Rho GTPase, is a serine/threonine protein kinase that regulates many crucial cellular processes via control of cytoskeletal structures. The C-terminal PH-C1 tandem of ROCKs has been implicated to play an autoinhibitory role by sequestering the N-terminal kinase domain and reducing its kinase activity. The binding of lipids to the pleckstrin homology (PH) domain not only regulates the localization of the protein but also releases the kinase domain from the close conformation and thereby activates its kinase activity. However, the molecular mechanism governing the ROCK PH-C1 tandem-mediated lipid membrane interaction is not known. In this study, we demonstrate that ROCK is a new member of the split PH domain family of proteins. The ROCK split PH domain folds into a canonical PH domain structure. The insertion of the atypical C1 domain in the middle does not alter the structure of the PH domain. We further show that the C1 domain of ROCK lacks the diacylglycerol/phorbol ester binding pocket seen in other canonical C1 domains. Instead, the inserted C1 domain and the PH domain function cooperatively in binding to membrane bilayers via the unconventional positively charged surfaces on each domain. Finally, the analysis of all split PH domains with known structures indicates that split PH domains represent a unique class of tandem protein modules, each possessing distinct structural and functional features.
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