Structural analysis of the G-box domain of the microcephaly protein CPAP suggests a role in centriole architecture.
Bottom Line: Centrioles are evolutionarily conserved eukaryotic organelles composed of a protein scaffold surrounded by sets of microtubules organized with a 9-fold radial symmetry.The G-box comprises a single elongated β sheet capable of forming supramolecular assemblies.Structural and biophysical studies highlight the conserved nature of the CPAP-STIL complex.
Affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK.Show MeSH
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Mentions: DrCPAPG-box consists of 17 antiparallel β strands that form a ∼75 Å long and ∼23 Å wide β sheet, with an ∼168° of twist across its length (Figures 2A and 2B). Remarkably, all residues of this structure are solvent exposed; thus, it lacks a well-defined hydrophobic core. A search for similar structures in the Protein Data Bank shows that only OspA, which features a large exposed β sheet (Makabe et al., 2006), is structurally related. However, DrCPAPG-box does not include globular domains capping the β sheet, in contrast to OspA, yet it remains highly soluble and cooperatively folded (Figure 1G). Analysis of the model suggests that DrCPAPG-box is stabilized through a number of interstrand ionic interactions (Figure 2C), as well as through clusters of hydrophobic residues that span multiple β strands (Figure 2D). In addition, significant burial of hydrophobic surface area occurs between nonpolar side chains and the aliphatic part of long polar groups, such as arginine and lysine residues. To better understand DrCPAPG-box stability, we performed a 100 ns atomistic molecular dynamics simulation starting from the crystallographic structure. As shown in Figure S2, DrCPAPG-box remains folded during the simulation with no signs of β sheet unraveling. The domain length (Figure S2A), the number of main chain hydrogen bonds formed (Figure S2B), and the hydrophobic area buried (Figure S2C) remain essentially unaltered throughout the simulation trajectory (Figure S2D; Movie S1).
Affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK.