Arabidopsis thaliana temperature-induced lipocalin (AtTIL) is a prototypical member of plant lipocalins and participates in a variety of cellular processes, particularly stress responses. Bioinformatical and physiological studies have proposed its promiscuous ligand-binding ability, but the molecular basis is yet unclear. Here, we report the 1.9-Å crystal structure of AtTIL in complex with heme. Spectrophotometric absorbance titration with heme yields a dissociation constant of ∼2 micromolar, indicating the relatively weak interaction between AtTIL and heme, which is confirmed by the AtTIL-heme structure. Although binding to retinal or biliverdin is not detected, such possibility can not be precluded as suggested by comparison with other lipocalin structures. These results show that AtTIL is a structural and functional homolog of the bacterial lipocalin Blc.

拟南芥温度诱导的脂质运载蛋白 (AtTIL) 是植物脂质运载蛋白的典型成员，参与多种细胞过程，特别是应激反应。生物信息和生理学研究提出了其混杂的配体结合能力，但其分子基础尚不清楚。在这里，我们报道了 AtTIL 与血红素复合物的 1.9-Å 晶体结构。血红素的分光光度吸光度滴定产生〜2微摩尔的解离常数，表明AtTIL和血红素之间的相互作用相对较弱，这由AtTIL-血红素结构证实。尽管未检测到与视网膜或胆绿素的结合，但如与其他脂质运载蛋白结构的比较所表明的，不能排除这种可能性。这些结果表明 AtTIL 是细菌脂质运载蛋白 Blc 的结构和功能同系物。