PDBsum entry 2c4c

Transport

PDB id: 2c4c

Contents

Protein chains

476 a.a.

Ligands

FAD ×2

Metals

_CL ×2

Waters ×40

References listed in PDB file

Key reference

Title

High-Resolution structure of the catalytic region of mical (molecule interacting with casl), A multidomain flavoenzyme-Signaling molecule.

Authors

C.Siebold, N.Berrow, T.S.Walter, K.Harlos, R.J.Owens, D.I.Stuart, J.R.Terman, A.L.Kolodkin, R.J.Pasterkamp, E.Y.Jones.

Ref.

Proc Natl Acad Sci U S A, 2005, 102, 16836-16841. [DOI no: 10.1073/pnas.0504997102]

PubMed id

16275925

Abstract

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-A 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 flavoenzyme 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.

Figure 3.
Fig. 3. Schematic representation of the FAD-apoprotein interactions in mMICAL[489]. View on the si face of the flavin with the FAD and interacting residues depicted as sticks [N, blue; O, red; P, violet; S, yellow; C (protein), orange; C (FAD), gray] and water molecules shown as cyan spheres. H bonds are shown in green with lengths in Å. Red "eyelashes" show hydrophobic interactions.

Figure 4.
Fig. 4. Comparison of the reduced and oxidized forms of mMICAL[489].(A and B) Superposition of the two forms. The FAD molecules are drawn as balls and sticks (carbons of oxidized mMICAL[489], cyan; carbons of reduced mMICAL[489], orange). The main chain of the oxidized form is depicted as a ribbon. B is rotated by 90° about the x axis relative to A. (C and D) Coordination of the isoalloxazine ring in the oxidized (C) and reduced (D) forms viewed from a common orientation. The isoalloxazine ring and selected residues are depicted as sticks (orange, carbon of reduced isoalloxazine; gray, protein carbon), waters are shown as spheres, and H bonds are shown as yellow dashes.