Cellular retinoic acid binding protein 2 (CRABP2) transports retinoic acid from the cytoplasm to the nucleus where it then transfers its cargo to retinoic acid receptor-containing complexes leading to activation of gene transcription. We demonstrate using purified proteins that CRABP2 is also a cyclin D3-specific binding protein and that the CRABP2 cyclin D3 binding site and the proposed CRABP2 nuclear localization sequence overlap. Both sequences are within the helix-loop-helix motif that forms a lid to the retinoic acid binding pocket. Mutations within this sequence that block both cyclin D3 and retinoic acid binding promote formation of a CRABP2 structure in which the retinoic acid binding pocket is occupied by an alternative lid conformation. Structural and functional analysis of CRABP2 and cyclin D3 mutants combined with AlphaFold models of the ternary CDK4/6-cyclin D3-CRABP2 complex supports the identification of an α-helical protein binding site on the cyclin D3 C-terminal cyclin box fold.

中文翻译：

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CRABP2 与细胞周期蛋白 D3 特异性结合的结构要求


细胞视黄酸结合蛋白 2 （CRABP2） 将视黄酸从细胞质转运到细胞核，然后将其货物转移到含有视黄酸受体的复合物上，从而导致基因转录激活。我们使用纯化的蛋白质证明 CRABP2 也是一种细胞周期蛋白 D3 特异性结合蛋白，并且 CRABP2 细胞周期蛋白 D3 结合位点和提出的 CRABP2 核定位序列重叠。两个序列都位于螺旋-环-螺旋基序内，该基序形成视黄酸结合口袋的盖子。该序列中阻断细胞周期蛋白 D3 和视黄酸结合的突变促进了 CRABP2 结构的形成，其中视黄酸结合口袋被另一种盖子构象占据。CRABP2 和细胞周期蛋白 D3 突变体的结构和功能分析与三元 CDK4/6-细胞周期蛋白 D3-CRABP2 复合物的 AlphaFold 模型相结合，支持在细胞周期蛋白 D3 C 末端细胞周期蛋白盒折叠上鉴定 α-螺旋蛋白结合位点。