Previous studies showed that cytochrome P450 1A2 (CYP1A2) forms a homomeric complex that influences its metabolic characteristics. Specifically, CYP1A2 activity exhibits a sigmoidal response as a function of NADPH-cytochrome P450 reductase (POR) concentration and is consistent with an inhibitory CYP1A2•CYP1A2 complex that is disrupted by increasing [POR] (Reed et al. (2012) Biochem. J. 446, 489–497). The goal of this study was to identify the CYP1A2 contact regions involved in homomeric complex formation. Examination of X-ray structure of CYP1A2 implicated the proximal face in homomeric complex formation. Consequently, the involvement of residues L91–K106 (P1 region) located on the proximal face of CYP1A2 was investigated. This region was replaced with the homologous region of CYP2B4 (T81–S96) and the protein was expressed in HEK293T/17 cells. Complex formation and its disruption was observed using bioluminescence resonance energy transfer (BRET). The P1-CYP1A2 (CYP1A2 with the modified P1 region) exhibited a decreased BRET signal as compared with wild-type CYP1A2 (WT-CYP1A2). On further examination, P1-CYP1A2 was much less effective at disrupting the CYP1A2•CYP1A2 homomeric complex, when compared with WT-CYP1A2, thereby demonstrating impaired binding of P1-CYP1A2 to WT-CYP1A2 protein. In contrast, the P1 substitution did not affect its ability to form a heteromeric complex with CYP2B4. P1-CYP1A2 also showed decreased activity as compared with WT-CYP1A2, which was consistent with a decrease in the ability of P1-CYP1A2 to associate with WT-POR, again implicating the P1 region in POR binding. These results indicate that the contact region responsible for the CYP1A2•CYP1A2 homomeric complex resides in the proximal region of the protein.
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Cover Image
Cover Image
PKA Cβ: A forgotten catalytic subunit of cAMP-dependent protein kinase opens new windows for PKA signaling and disease pathologies.
The N- and C-terminal tails (Nt-tail/Ct-Tail) of the PKA catalytic subunit wrap around the N-lobe (white shell) and C-lobe (tan shell) of the kinase core. The sequences differences, indicated as dots, between Cα and Cβ are mapped onto the Cα structure, these cluster around the Nt-Tail and the Ct-Tail and to regions of the core that are regulated by the tails. The Cβ isoforms created by different genes and splice variants differ only in the first exon (circle), a region in Cα that is important for targeting. For more information see the review by Taylor and colleagues (pp. 2101–2119) in this issue. Image provided by Susan Taylor.
Identification of the contact region responsible for the formation of the homomeric CYP1A2•CYP1A2 complex
