In the past years, Prof. DING Jianping’s group from the National Center for Protein Science, Shanghai, Institute of Biochemistry and Cell Biology (SIBCB), Shanghai Institutes for Biological Sciences (SIBS), Chinese Academy of Sciences (CAS), has carried out the structural and functional studies of several important proteins involved in the vesicle-mediated transport process.
Very recently, Ph.D. candidate WANG Rong and her colleagues in Prof. DING Jianping’s group made another progress in elucidating the molecular basis for targeting BIG1 to Golgi apparatus by Arl1. This work was published in Journal of Molecular Cell Biology.
Endocytosis is an energy-using process by which cells absorb macromolecules and particles and controls entry into the cell. The ADP ribosylation factor (Arf) family of small GTPases functions as molecular switches to modulate vesicular and lipid trafficking in cell membrane traffic.Human BIG1 belongs to the Sec7 domain-containing Arf GEFs, which functions mainly on the trans-Golgi to activate Arf proteins from the GDP-bound form to GTP-bound form. Arl1 was suggested to direct BIG1 to the trans-Golgi through interaction with BIG1, and then activate the Arf-dependent pathway in a cascade manner. However, the molecular basis for the specific recognition and recruitment of BIG1 by Arl1 remains unknown.
The researchers determined the crystal structure of the GTP-bound Arl1 in complex with the N-terminal dimerization and cyclophilin binding (DCB) domain of BIG1. In the structure, the DCB domain adopts a HEAT repeat fold, with the four HEAT repeats forming a short arc to embrace Arl1. The Arl1-GTP assumes a typical small GTPase fold and interacts with the DCB domain mainly via the switch I, switch II and interswitch regions. The binding mode between Arl1 and DCB is unique and greatly different from other Arl1-effector complexes.
Structural and biochemical analyses, including GST pull-down and co-localization assays, revealed several key residues essential for the binding. They also analyzed the binding specificity of the BIG1 DCB domain with several Arl small GTPases and identified Arl4a as a binding partner of BIG1. Based on these results, they proposed a working model for targeting BIG1 to the trans-Golgi via interaction of DCB domain with Arl1-GTP.
These findings also advance our knowledge in understanding the functions of the Arf small GTPases and their specific GEFs and the regulation of the Arf-dependent pathway in endocytosis and vesicular trafficking.
The research work entitled “Structural basis for targeting BIG1 to Golgi apparatus through interaction of its DCB domain with Arl1” was published online in the Journal of Molecular Cell Biology on July 19th, 2016.
This study is supported by grants from the National Natural Science Foundation of China and the Chinese Academy of Sciences. The X-ray diffraction data used in the structure determination were acquired at beamline 19U of National Facility for Protein Science in Shanghai.
AUTHOR CONTACT:
DING Jianping, Ph.D., Professor
National Center for Protein Science Shanghai, State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences
320 Yueyang Road, Shanghai 200031, China
Tel: 86-21-54921619
Email: jpding@sibs.ac.cn
KEYWORDS: Arl1, BIG1, GEF, small GTPase
NEWS ABSTRACT:
This study reports the crystal structure of small GTPase Arl1-GTP in complex with the effector protein BIG1. The structure reveals that the DCB domain adopts a HEAT repeat fold and interacts specifically with the GTP-bound Arl1. Structural data together with biochemical and cell biological data reveal the molecular basis for the specific interaction of Arl1 with BIG1 and provide insight into the molecular mechanism for targeting BIG1 to the trans-Golgi by Arl1.
Working model for targeting BIG1 to the trans-Golgi via interaction of its DCB domain with Arl1-GTP. The membrane localized Arl1-GTP interacts directly with the DCB domain of BIG1 and recruits BIG1 to the trans-Golgi, and hence the Sec7 domain of BIG1 can exert the GEF activity towards and activate the Arf proteins. The activated Arf proteins can thus recruit the effectors such as coat complexes to the trans-Golgi, leading to the activation of the downstream trafficking pathway. (Image provided by Prof. DING Jianping's group)
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