Crystallization and preliminary X-ray crystallographic analysis of human PACSIN 1 protein

Rigidity of wedge loop in PACSIN 3 protein is a key factor in dictating diameters of tubules

BAR (Bin/amphiphysin/Rvs) domain-containing proteins participate in cellular membrane remodeling. The F-BAR proteins normally generate low curvature tubules. However, in the PACSIN subfamily, the F-BAR domain from PACSIN 1 and 2 can induce both high and low curvature tubules. We found that unlike PACSIN 1 and 2, PACSIN 3 could only induce low curvature tubules. To elucidate the key factors that dictate the tubule curvature, crystal structures of all three PACSIN F-BAR domains were determined. A novel type of lateral interaction mediated by a wedge loop is observed between the F-BAR neighboring dimers. Comparisons of the structures of PACSIN 3 with PACSIN 1 and 2 indicate that the wedge loop of PACSIN 3 is more rigid, which influences the lateral interactions between assembled dimers. We further identified the residues that affect the rigidity of the loop by mutagenesis and determined the structures of two PACSIN 3 wedge loop mutants. Our results suggest that the rigidity-mediated conformations of the wedge loop correlate well with the various crystal packing modes and membrane tubulations. Thus, the rigidity of the wedge loop is a key factor in dictating tubule diameters.

Cloning, purification, crystallization and preliminary X-ray diffraction analysis of mouse PACSIN 3 protein

PACSIN-family proteins are cytoplasmic proteins that have vesicle-transport, membrane-dynamics, actin-reorganization and microtubule activities. Here, the N-terminal F-BAR domain of mouse PACSIN 3, which contains 341 amino acids, was successfully cloned, purified and crystallized. The crystal of PACSIN 3 (1-341) diffracted to 2.6 Å resolution and belonged to space group P2(1), with unit-cell parameters a = 46.9, b = 54.7, c = 193.7 Å, α = 90, β = 96.9, γ = 90°. These data should provide further information on PACSIN-family protein structures.

Protein expression, crystallization and preliminary X-ray crystallographic studies of LidA from Legionella pneumophila

LidA, a translocated substrate of the Legionella pneumophila Dot/Icm type IV secretion system, is associated with maintenance of bacterial integrity and interferes with the early secretory pathway. However, the precise mechanism of LidA in these processes remains elusive. To further investigate the structure and function of LidA, the full-length protein was successfully expressed in Escherichia coli and purified. LidA was crystallized using sitting-drop vapour diffusion and diffracted to a resolution of 2.75 Å. The crystal belonged to space group P2(1)2(1)2(1), with unit-cell parameters a = 57.5, b = 64.5, c = 167.3 Å, α = β = γ = 90°. There is one molecule per asymmetric unit.

A hinge in the distal end of the PACSIN 2 F-BAR domain may contribute to membrane-curvature sensing

The protein kinase C and casein kinase 2 substrates in neurons (PACSINs) represent a subfamily of membrane-binding proteins characterized by an amino-terminal Bin-Amphiphysin-Rvs (F-BAR) domain. PACSINs link membrane trafficking with actin dynamics and regulate the localization of distinct cargo molecules. The F-BAR domain forms a dimer essential for lipid binding. We have obtained crystals of authentic murine PACSIN 2 that contain an ordered F-BAR domain, indicating that additional domains are flexibly connected to F-BAR. The structure shares similarity to other BAR domains and exhibits special features unique to PACSINs. These include the uneven distribution of charged residues on the concave molecular surface and a so-called wedge loop that is driven into the membrane upon binding of PACSIN. The murine PACSIN 2 F-BAR domain requires dimerization for sensing of curved membranes, and the present structure also provides a mechanism for higher-order oligomer formation. Importantly, comparison of murine with human and Drosophila PACSIN 2 F-BAR domains reveals stark differences in the orientation of distal helical segments leading to a wider crescent shape of murine PACSIN 2. We define hinge residues for these movements that may help PACSINs sense and concomitantly reinforce membrane curvature.