A research team at The Hong Kong University of Science and Technology (HKUST) has made significant strides in understanding cellular protein transport mechanisms. Led by Prof. Guo Yusong, an Associate Professor in the Division of Life Science, the team has identified crucial protein transport processes linked to several genetic diseases. Their findings were published in the Proceedings of the National Academy of Sciences (PNAS).
Utilizing a novel vesicle proteomics platform, the researchers systematically pinpointed new cargo proteins and essential accessory factors for critical cellular transport complexes, specifically AP-1 and AP-4. The study combines advanced vesicle reconstitution techniques with quantitative mass spectrometry-based proteomics, resulting in a detailed map of previously unidentified cargo proteins and regulatory factors.
Understanding the Secretory Pathway
The cellular secretory pathway functions like a postal service, ensuring proteins reach their designated locations to maintain cellular functionality. Errors in this transport system can lead to severe physiological defects and are implicated in conditions such as MEDNIK syndrome and X-linked intellectual disability.
“For years, the field has struggled to comprehensively map the cargo repertoire of adaptor complexes like AP-1 and AP-4,” stated Prof. Guo. “Malfunctions in these complexes are directly linked to serious human conditions. However, the full list of proteins they transport has remained elusive.” He emphasized that the study marks a transformative advancement by reconstituting the transport process in vitro and applying quantitative proteomics. This innovative approach allowed the team to identify which proteins depend on AP-1 or AP-4 for their vesicular packaging, moving beyond a fragmented understanding to a more cohesive view of their cargo landscape.
The research confirmed that the protein CAB45 relies on AP-1 for transport, while ATRAP emerged as a novel cargo for AP-4. A pivotal discovery of this study addresses a longstanding question regarding how AP-4 forms transport vesicles without the well-known protein clathrin.
Key Discoveries and Future Implications
The researchers found that two cytosolic factors, WDR44 and PRRC1, are critical for AP-4-mediated trafficking. When these factors were depleted, vital AP-4 cargoes like ATG9A and ATRAP were unable to exit their organelles, causing disruptions in essential cellular processes, including autophagy.
“Our findings not only reveal new cargo clients and essential co-factors for AP-1 and AP-4 but also provide a powerful toolkit for the scientific community to dissect the mechanisms of vesicular trafficking,” Prof. Guo added. “This opens new avenues for researching the pathological mechanisms of related diseases and potentially identifying new therapeutic targets.”
The co-corresponding authors of this transformative research are Prof. Guo Yusong of HKUST and Prof. Yao Zhong-Ping of The Hong Kong Polytechnic University (PolyU). The first author of the study is Dr. Peng Ziqing, a postdoctoral researcher at HKUST.
This groundbreaking research not only enhances our understanding of cellular transport mechanisms but also sets the stage for future studies that could lead to innovative therapeutic strategies for genetic diseases linked to these transport processes.
