High-Resolution Structure of the Catalytic Region of MICAL (Molecule Interacting with CasL), a Multidomain Flavoenzyme-Signaling Molecule

• Published in: Proceedings of the National Academy of Sciences - PNAS 2005-11, Vol.102 (46), p.16836-16841
• Main Authors: Siebold, Christian, Nick Berrow, Thomas S. Walter, Harlos, Karl, Ray J. Owens, Stuart, David I., Terman, Jonathan R., Kolodkin, Alex L., R. Jeroen Pasterkamp, Jones, E. Yvonne
• Format: Article
• Language: English
• Subjects: Active sites; Animals; Atoms; Binding Sites; Biological Sciences; Catalysis; Catalytic Domain; Chemical reactions; Crystal structure; Crystallization; Enzymes; Flavin-Adenine Dinucleotide - metabolism; Flavins - chemistry; Flavins - metabolism; Flavoproteins; Hydrogen bonds; Mice; Microtubule-Associated Proteins - chemistry; Microtubule-Associated Proteins - metabolism; Mixed Function Oxygenases - chemistry; Mixed Function Oxygenases - metabolism; Models, Molecular; Molecular interactions; Molecular structure; Molecules; NADP - metabolism; Oxidation-Reduction; Oxygen; Protein Conformation; Proteins; Signal Transduction
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0504997102

Semaphorins are extracellular cell guidance cues that govern cytoskeletal dynamics during neuronal and vascular development. MICAL (molecule interacting with CasL) is a multidomain cytosolic protein with a putative flavoprotein monooxygenase (MO) region required for semaphorin-plexin repulsive axon guidance. Here, we report the 1.45-Å resolution crystal structure of the FAD-containing MO domain of mouse MICAL-1 (residues 1-489). The topology most closely resembles that of the NADPH-dependent f lavoenzyme p-hydroxybenzoate hydroxylase (PHBH). Comparison of structures before and after reaction with NADPH reveals that, as in PHBH, the flavin ring can switch between two discrete positions. In contrast with other MOs, this conformational switch is coupled with the opening of a channel to the active site, suggestive of a protein substrate. In support of this hypothesis, distinctive structural features highlight putative protein-binding sites in suitable proximity to the active site entrance. The unusual juxtaposition of this N-terminal MO (hydroxylase) activity with the characteristics of a multiprotein-binding scaffold exhibited by the C-terminal portion of the MICALs represents a unique combination of functionality to mediate signaling.