Wu Jingyi, Wan Chun, Tian Yuan, Ouyang Yan, Puscher Harrison, Li Suzhao, Yin Qian, Shen Jingshi
Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO 80309, USA.
Department of Biological Sciences and Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA.
Sci Adv. 2025 Sep 12;11(37):eadw9158. doi: 10.1126/sciadv.adw9158.
A critical yet challenging step in protein complex assembly is the formation of a dimeric intermediate that serves as a seed for incorporating additional subunits. We hypothesized that this step could be facilitated by "bi-handed" chaperones that recognize two different subunits through distinct domains (hands). However, whether such chaperones exist remained unknown. Here, we identify AAGAB as a bona fide bi-handed chaperone. AAGAB uses its C-terminal domain (CTD) to bind the α subunit and its GTPase-like domain (GD) to bind the σ2 subunit of the AP2 adaptor complex, a central player in membrane trafficking. AAGAB first recruits α via its CTD; σ2 then joins through interaction with α, forming a conformationally immature α:σ2 hemicomplex at the CTD. This hemicomplex is subsequently transferred to the GD via a GD:σ2 binding interface, accompanied by conformational maturation. These findings establish AAGAB as the founding member of a bi-handed chaperone family and reveal an intramolecular handover mechanism that underlies their mode of action.
蛋白质复合物组装过程中关键且具有挑战性的一步是形成二聚体中间体，该中间体作为纳入其他亚基的种子。我们推测这一步骤可能由“双手性”伴侣蛋白促进，这些伴侣蛋白通过不同结构域（手）识别两种不同的亚基。然而，此类伴侣蛋白是否存在仍不清楚。在此，我们鉴定出AAGAB是一种真正的双手性伴侣蛋白。AAGAB利用其C端结构域（CTD）结合α亚基，并利用其GTP酶样结构域（GD）结合AP2衔接复合物的σ2亚基，AP2衔接复合物是膜运输中的核心参与者。AAGAB首先通过其CTD招募α；然后σ2通过与α相互作用加入，在CTD处形成构象不成熟的α:σ2半复合物。随后，该半复合物通过GD:σ2结合界面转移至GD，同时伴随构象成熟。这些发现确立了AAGAB作为双手性伴侣蛋白家族的创始成员，并揭示了其作用方式背后的分子内交接机制。
