Department of Pharmaceutics, School of Pharmacy, University of Washington, Seattle, WA 98195, USA.
Nutrients. 2022 Apr 24;14(9):1784. doi: 10.3390/nu14091784.
Cellular retinoic acid binding proteins (CRABP1 and CRABP2) bind -retinoic acid (RA), the active metabolite of vitamin A, with high affinity. CRABP1 and CRABP2 have been shown to interact with the RA-clearing cytochrome P450 enzymes CYP26B1 and CYP26C1 and with nuclear retinoic acid receptors (RARs). We hypothesized that CRABP1 and CRABP2 also alter RA metabolism and clearance by CYP26A1, the third key RA-metabolizing enzyme in the CYP26 family. Based on stopped-flow experiments, RA bound CRABP1 and CRABP2 with K values of 4.7 nM and 7.6 nM, respectively. The unbound RA K values for 4-OH-RA formation by CYP26A1 were 4.7 ± 0.8 nM with RA, 6.8 ± 1.7 nM with holo-CRABP1 and 6.1 ± 2.7 nM with holo-CRABP2 as a substrate. In comparison, the apparent k value was about 30% lower (0.71 ± 0.07 min for holo-CRABP1 and 0.75 ± 0.09 min for holo-CRABP2) in the presence of CRABPs than with free RA (1.07 ± 0.08 min). In addition, increasing concentrations in apo-CRABPs decreased the 4-OH-RA formation rates by CYP26A1. Kinetic analyses suggest that apo-CRABP1 and apo-CRABP2 inhibit CYP26A1 (K = 0.39 nM and 0.53 nM, respectively) and holo-CRABPs channel RA for metabolism by CYP26A1. These data suggest that CRABPs play a critical role in modulating RA metabolism and cellular RA concentrations.
细胞视黄酸结合蛋白 (CRABP1 和 CRABP2) 与视黄酸 (RA) 即维生素 A 的活性代谢物具有高亲和力。CRABP1 和 CRABP2 已被证明与 RA 清除细胞色素 P450 酶 CYP26B1 和 CYP26C1 以及核视黄酸受体 (RAR) 相互作用。我们假设 CRABP1 和 CRABP2 也通过 CYP26 家族中的第三个关键 RA 代谢酶 CYP26A1 改变 RA 代谢和清除。基于停流实验，RA 分别以 4.7 nM 和 7.6 nM 的 K 值结合 CRABP1 和 CRABP2。CYP26A1 形成 4-OH-RA 时，RA 的未结合 RA K 值分别为 4.7 ± 0.8 nM、CRABP1 全酶的 6.8 ± 1.7 nM 和 CRABP2 全酶的 6.1 ± 2.7 nM。相比之下，在 CRABP 存在的情况下，表观 k 值约低 30%（CRABP1 全酶为 0.71 ± 0.07 min，CRABP2 全酶为 0.75 ± 0.09 min），而游离 RA 的 k 值为 1.07 ± 0.08 min。此外，apo-CRABP 的浓度增加会降低 CYP26A1 形成 4-OH-RA 的速率。动力学分析表明，apo-CRABP1 和 apo-CRABP2 抑制 CYP26A1（K = 0.39 nM 和 0.53 nM），而全酶形式的 CRABP 则为 CYP26A1 代谢 RA 提供通道。这些数据表明，CRABP 在调节 RA 代谢和细胞内 RA 浓度方面起着关键作用。
