Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, VIC 3052, Australia.
Acta Crystallogr F Struct Biol Commun. 2021 May 1;77(Pt 5):140-147. doi: 10.1107/S2053230X21004489. Epub 2021 Apr 30.
The Atg8 protein family comprises the GABA type A receptor-associated proteins (GABARAPs) and microtubule-associated protein 1 light chains 3 (MAP1LC3s) that are essential mediators of autophagy. The LC3-interacting region (LIR) motifs of autophagy receptors and adaptors bind Atg8 proteins to promote autophagosome formation, cargo recruitment, and autophagosome closure and fusion to lysosomes. A crystal structure of human GABARAPL2 has been published [PDB entry 4co7; Ma et al. (2015), Biochemistry, 54, 5469-5479]. This was crystallized in space group P2 with a monoclinic angle of 90° and shows a pseudomerohedral twinning pathology. This article reports a new, untwinned GABARAPL2 crystal form, also in space group P2, but with a 98° monoclinic angle. No major conformational differences were observed between the structures. In the structure described here, the C-terminal Phe117 binds into the LIR docking site (LDS) of a neighbouring molecule within the asymmetric unit, as observed in the previously reported structure. This crystal contact blocks the LDS for co-crystallization with ligands. Phe117 of GABARAPL2 is normally removed during biological processing by Atg4 family proteases. These data indicate that to establish interactions with the LIR, Phe117 should be removed to eliminate the crystal contact and liberate the LDS for co-crystallization with LIR peptides.
Atg8 蛋白家族包括 GABA 型 A 受体相关蛋白（GABARAPs）和微管相关蛋白 1 轻链 3（MAP1LC3s），它们是自噬的重要介质。自噬受体和衔接蛋白的 LC3 相互作用区域（LIR）基序与 Atg8 蛋白结合，以促进自噬体的形成、货物的募集以及自噬体的闭合和与溶酶体融合。已经发表了人 GABARAPL2 的晶体结构 [PDB 条目 4co7；Ma 等人，（2015），生物化学，54，5469-5479]。该晶体在空间群 P2 中结晶，具有 90°的单斜角，显示出拟多晶二态病理学。本文报道了一种新的、未扭曲的 GABARAPL2 晶体形式，同样在空间群 P2 中，但具有 98°的单斜角。结构之间没有观察到主要的构象差异。在本文所描述的结构中，C 端的 Phe117 结合到不对称单元中相邻分子的 LIR 对接位点（LDS）中，如先前报道的结构中所观察到的。这种晶体接触阻止了 LDS 与配体共结晶。在生物加工过程中，GABARAPL2 的 Phe117 通常被 Atg4 家族蛋白酶切除。这些数据表明，为了与 LIR 建立相互作用，Phe117 应该被切除以消除晶体接触并释放 LDS 以与 LIR 肽共结晶。
