• Daniel A. Kramer, Heidy Y. Narvaez-Ortiz, Urval Patel, Rebecca Shi, Kang Shen, Brad J. Nolen,  Julien Roche#, Baoyu Chen#. The intrinsically disordered cytoplasmic tail of a dendrite branching receptor uses two distinct mechanisms to regulate the actin cytoskeleton. eLife (2023, in press)​. also in: BioRxiv 491788v3 [Preprint]. April 12, 2023.
Dual functions of the disordered tail of the dendrite branching receptor HPO-30
Dendrite morphogenesis is essential to neural circuit formation, but the molecular mechanisms controlling the growth of complicated dendrite branches are not well understood. This work sheds light on the cytoplasmic tail of the dendrite branching receptor HPO-30, which we found uses two distinct mechanisms to coordinate actin cytoskeletal remodeling: A) using a novel mechanism to bind the WAVE complex (WRC), which promotes Arp2/3-mediated actin polymerization, and B) binding to the barbed end of actin filaments, which resembles the actin capping protein CapZ. These two mechanisms may act synergistically to assist Arp2/3 in generating complex branched actin networks necessary for initiating the outgrowth of new dendrite branches.
  • Sabrina Schlienger,  Patricia T. Yam,  Nursen Balekoglu, Hugo Ducuing,  Jean-Francois Michaud, Shirin Makihara, Daniel A. Kramer, Baoyu Chen, Alfonso Fasano,  Alfredo Berardelli, Fadi F. Hamdan, Guy A. Rouleau, Myriam Srour,  Frederic Charron. Genetics of mirror movements identifies a multifunctional complex required for Netrin-1 guidance and lateralization of motor control. Science Advances. 19 (9) add5501. (2023)
  • Sheng Yang, Yubo Tang*, Yijun Liu*, Abbigale J. Brown, Matthias Schaks, Bojian Ding, Daniel A. Kramer, Magdalena Mietkowska, Li Ding, Olga Alekhina, Daniel D. Billadeau, Saikat Chowdhury, Junmei Wang, Klemens Rottner# and Baoyu Chen#. Arf GTPase activates the WAVE Regulatory Complex through a distinct binding site. Science Advances. 50 (8) add1412. (2022) (PDF)
Arf GTPase is a second WRC activator
The Rho-family GTPase Rac1 has been long considered as the only genuine activator of the WAVE complex (WRC), being both necessary and sufficient to promote Arp2/3-mediated actin polymerization in cells. Now our biochemical reconstitution establishes the Arf-family GTPases as a second, bona fide activator of WRC. This work finds that Arf directly binds to WRC at a novel, conserved site, which is sufficient to trigger WRC activation independent of Rac1-mediated mechanism. This finding opens the door for studying how WRC integrates Arf and Rac signaling pathways to regulate the actin cytoskeleton.
  • Karina Chaudhari, Kaiyue Zhang, Patricia T. Yam, Yixin Zang, Daniel A. Kramer, Sabrina Schlienger, Sara Calabretta, Myriam Srour, Baoyu Chen, Frédéric Charron and Greg J. Bashaw. A human DCC variant causing mirror movement disorder reveals an essential role for the Wave regulatory complex in Netrin/DCC signaling. BioRxiv 511954 [Preprint]. October 17, 2022.
  • Bojian Ding*, Sheng Yang*, Matthias Schaks, Yijun Liu, Abbigale J. Brown,  Klemens Rottner, Saikat Chowdhury# and Baoyu Chen#. Structures reveal a key mechanism of WAVE Regulatory Complex activation by Rac1 GTPase. Nature Communications. 13, 5444. (2022) (PDF)
WRC activation mechanism unveiled
Cryo-EM structures of the WAVE complex (WRC) in three different states—by itself, with Rac1 bound to the D site, and with two Rac1 molecules bound to both the A and D sites simultaneously—reveal Rac1 binding to the A site, but not the D site, directly triggers a conformational change, which propagates to a conserved region surrounding Y151 of WAVE1 to destabilize the meander sequence and release the sequestered WCA domain, leading to WRC activation.
A detailed introduction of the Wiskott-Aldrich syndrome protein (WASP) family proteins 
  • Anna Polesskaya, Arthur Boutillon, Sheng Yang, Yanan Wang, Stéphane Romero, Yijun Liu, Marc Lavielle, Sophie Vacher, Anne Schnitzler, Nicolas Molinie, Nathalie Rocques, Artem Fokin, Raphaël Guérois, Ivan Bièche, Baoyu Chen, Nicolas B. David, Alexis M. Gautreau. CYFIP2-containing WAVE complexes inhibit cell migration by a competition mechanism. BioRxiv 184655 [Preprint]. August 21, 2021.
  • Rebecca Shi, Daniel A. Kramer, Baoyu Chen, Kang Shen. A two-step actin polymerization mechanism drives dendrite branching. Neural Development. 16(1):3. (2021)  (PDF)​​
A primer of the WAVE regulatory complex (WRC): biochemistry and structure, biology and disease.
  • Sarah A. Cook, William A. Comrie, M. Cecilia Poli, Morgan Similuk, Andrew J. Oler, Aiman J. Faruqi, Douglas B. Kuhns, Sheng Yang, Alexander Vargas-Hernández, Alexandre F. Carisey, Benjamin Fournier, D. Eric Anderson, Susan Price, Margery Smelkinson, Wadih Abou Chahla, Lisa R. Forbes, Emily M. Mace, Tram N. Cao, Zeynep H. Coban-Akdemir, Shalini N. Jhangiani, Donna M. Muzny, Richard A. Gibbs, James R. Lupski, Jordan S. Orange, Geoffrey D. E. Cuvelier, Moza Al Hassani, Nawal Al Kaabi, Zain Al Yafei, Soma Jyonouchi, Nikita Raje, Jason W. Caldwell, Yanping Huang, Janis K. Burkhardt, Sylvain Latour, Baoyu Chen, Gehad ElGhazali, V. Koneti Rao, Ivan K. Chinn, Michael J. Lenardo. HEM1 deficiency disrupts mTORC2 and F-actin control in inherited immunodysregulatory disease. ​Science. 369 (6500): 202-207. (2020) (PDF)
Genetic mutations in the WRC cause immune disease
Mutations in the gene NCKAP1L, encoding the hematopoietic-specific Hem1 subunit of the WAVE Regulatory Complex (WRC), were identified in patients from four different families to cause a syndrome that combines both immune deficiency and hyperresponsiveness. The mutations either compromised the stability of the WRC or impaired its activation by the Arf1 GTPase, which, consequently, disrupted a wide range of immune cell functions, including actin polymerization, synapse formation, cell migration, cytokine release, mTORC2-dependent AKT phosphorylation, and T cell proliferation.
  • Jing Wang, Alina Fedoseienko, Baoyu Chen, Ezra Burstein, Da Jia, Daniel D. Billadeau. Endosomal Receptor Trafficking: Retromer and Beyond. ​Traffic. 19(8):​ 578-590. (2018) (PDF)
  • Wei Zou#, Xintong Dong, Timothy R. Broederdorf, Ao Shen, Daniel A. Kramer, Rebecca Shi, Xing Liang, David M. Miller III, Yang K. Xiang, Ryohei Yasuda, Baoyu Chen#, and Kang Shen#. A Dendritic Guidance Receptor Complex Brings Together Distinct Actin Regulators to Drive Efficient F-Actin Assembly and Branching. ​Developmental Cell. 45 (3) 362–375.e3 (2018) (# Co-corresponding authors) (PDF)
Teamwork drives neuron morphogenesis 
​Neurons grow highly branched dendrites to establish complex neural circuits in animals. However, how dendrites develop the branched structures is largely unknown. This work reveals that in the PVD sensory neuron of the nematode worm C. elegans, formation of high-order dendrite branches requires F-actin assembly driven by teamwork of two membrane proteins and two actin regulators. The first membrane protein DMA-1, which determines the sites of branching by forming a ligand-receptor complex with three epidermis/muscle-specific ligands (SAX-7, MNR-1 and LECT-2), directly binds to an actin regulator named TIAM-1, which can promote actin assembly by activating the GTPase Rac. The second membrane protein, a claudin-like protein named HPO-30, directly interacts with the WAVE Regulatory Complex (WRC), a central actin regulator which can be activated by Rac to promote F-actin assembly. On dendrites, DMA-1 and HPO-30 form a signaling complex to bring TIAM-1 and the WRC to close proximity to specifically enhance F-actin assembly, which, in turn, drives high-order dendrite branching. Different neurons may use a similar strategy, albeit likely by coordinating distinct sets of receptors and actin regulators, to synergistically activate F-actin assembly and promote complex dendrite arborization. 
  • Baoyu Chen#, Hui-Ting Chou, Chad A Brautigam, Wenmin Xing, Sheng Yang, Lisa Henry, Lynda K Doolittle, Thomas Walz and Michael K Rosen#. Rac1 GTPase activates the WAVE regulatory complex through two distinct binding sites. eLife. 6:e29795 (2017) (# Co-corresponding authors) (PDF)
One safe box, two keys
​The Rho GTPase Rac1 activates the WAVE Regulatory Complex (WRC) to release the VCA peptide. The VCA, in turn, stimulates the Arp2/3 complex to assemble new actin filaments. This process is essential to various activities, including cell movement and morphogenesis. However, how Rac1 interacts with the WRC and activates it was unknown. This work solved the first structure of the WRC bound to Rac1 by using cryo-electron microscopy. The structure revealed an unexpected Rac1 binding site on the WRC, which is distant from a previously identified site.  Biochemical data suggest that activating the WRC to release the VCA requires two Rac1 molecules to bind to both sites at the same time. Cells may use this mechanism to precisely control WRC activation and thereby actin assembly, similar to using two keys to open a safe box for increased security. 
  • Xing Judy Chen, Anna Julia Squarr*, Raiko Stephan*, Baoyu Chen*, Theresa E. Higgins, David J. Barry, Morag C. Martin, Michael K. Rosen, Sven Bogdan and Michael Way. Ena/VASP proteins cooperate with the WAVE complex to regulate the actin cytoskeleton. Developmental Cell. 30 (5), 569-584. (2014) (PDF)
  • Baoyu Chen, Klaus Brinkmann, Zhucheng Chen, Chi W. Pak, Yuxing Liao, Shuoyong Shi, Lisa Henry, Nick Grishin, Sven Bogdan, and Michael K. Rosen. The WAVE regulatory complex links diverse receptors to the actin cytoskeleton. Cell. 156 (1-2), 195-207. (2014) (PDF)
Revelation of a signaling hub between membranes and actin
Membrane molecules allow the cell to sense and respond to external signals to make the right decisions. This process usually requires reorganizing the actin cytoskeleton underneath the membranes so that cells can move and change shape. For many membrane proteins, little is known how they instruct actin reorganization. This study revealed that the WAVE regulatory complex (WRC) acts as a central signaling hub by connecting numerous membrane proteins to actin. These membrane molecules have diverse functions and include adhesion receptors, ion channels, GPCRs and scaffolding proteins. They all contain a short peptide motif in their intracellular regions, which we named the WRC interacting receptor sequence (WIRS). The WIRS peptide binds to a conserved surface on the WRC. Through this interaction, membrane proteins can recruit the WRC to their sites of action to activate actin polymerization. Many laboratories have now shown that this signaling pathway plays diverse roles in animals, ranging from cell migration and neuron morphogenesis to cell adhesion and endocytosis. 
  • Pilong Li, Sudeep Banjade, Hui-Chun Cheng, Soyeon Kim, Baoyu Chen, Liang Guo, Marc LIaguno, Javoris V. Hollingsworth, David S. King, Salman F. Banani, Paul S. Russo, Qiu-Xing Jiang, B. Tracy Nixon, and Michael K. Rosen. Phase transitions in the assembly of multivalent signaling proteins. Nature. 483 (7389), 336-340. (2012) (PDF)
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  •  Baoyu Chen, Tatyana A. Syseova, Saikat Chowdhury, Liang Guo, and B. Tracy Nixon. ADPase activity of recombinantly expressed thermotolerant ATPases may be caused by copurification of adenylate kinase of Escherichia coli. FEBS Journal. 276(3): 807-815. (2009) (PDF)
  • Baoyu Chen, Michaeleen Doucleff, David E. Wemmer, Sacha De Carlo, Hector H. Huang, Eva Nogales, Timothy R. Hoover, Elena Kondrashkina, Liang Guo and B. Tracy Nixon. ATP ground- and transition states of bacterial enhancer binding AAA+ ATPases support complex formation with their target protein, s54. Structure. 15(4): 429-220. (2007) (PDF)
  • Sacha De Carlo*, Baoyu Chen*, Timothy R. Hoover, Elena Kondrashkina, Eva Nogales, and B. Tracy Nixon. The structural basis for regulated assembly and function of the transcriptional activator NtrC. Genes & Development. 20: 1485-1495. (2006) (PDF)
  • Michaeleen Doucleff, Baoyu Chen, Ann E. Maris, David E. Wemmer, Elena Kondrashkina and B. Tracy Nixon. Negative regulation of AAA+ ATPase assembly by two component receiver domains: a transcription activation mechanism that is conserved in mesophilic and extremely hyperthermophilic bacteria. Journal of Molecular Biology. 353: 242-255. (2005) (PDF)
  • Qin Guo, Baoyu Chen and Xicheng Wang. Evidence for proximal cysteine and lysine residues at or near the active site of arginine kinase of Stichopus japonicus. Biochemistry (Moscow). 69:1336-1343. (2004)
  • Suyuan Guo, Zhi Guo, Qin Guo, Baoyu Chen and Xicheng Wang. Expression, purification, and characterization of arginine kinase from the sea cucumber Stichopus japonicus. Protein Expression & Purification. 29: 230-234. (2003)
Roy J. Carver Department of Biochemistry, Biophysics & Molecular Biology, Iowa State University, Ames, Iowa, 50014.
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