Nicholas Burton

The Moraxella adhesin UspA1 binds to its human CEACAM1 receptor by a deformable trimeric coiled‐coil

Moraxella catarrhalis is a ubiquitous human‐specific bacterium commonly associated with upper and lower respiratory tract infections, including otitis media, sinusitis and chronic obstructive pulmonary disease. The bacterium uses an autotransporter protein UspA1 to target an important human cellular receptor carcinoembryonic antigen‐related cell adhesion molecule 1 (CEACAM1). Using X‐ray crystallography, we show that the CEACAM1 receptor‐binding region of UspA1 unusually consists of an extended, rod‐like left‐handed trimeric coiled‐coil. Mutagenesis and binding studies of UspA1 and the N‐domain of CEACAM1 have been used to delineate the interacting surfaces between ligand and receptor and guide assembly of the complex. However, solution scattering, molecular modelling and electron microscopy analyses all indicate that significant bending of the UspA1 coiled‐coil stalk also occurs. This explains how UspA1 can engage CEACAM1 at a site far distant from its head group, permitting closer proximity of the respective cell surfaces during infection.

Stomatin-deficient cryohydrocytosis results from mutations in SLC2A1: a novel form of GLUT1 deficiency syndrome

The hereditary stomatocytoses are a series of dominantly inherited hemolytic anemias in which the permeability of the erythrocyte membrane to monovalent cations is pathologically increased. The causative mutations for some forms of hereditary stomatocytosis have been found in the transporter protein genes, RHAG and SLC4A1. Glucose transporter 1 (glut1) deficiency syndromes (glut1DSs) result from mutations in SLC2A1, encoding glut1. Glut1 is the main glucose transporter in the mammalian blood-brain barrier, and glut1DSs are manifested by an array of neurologic symptoms. We have previously reported 2 cases of stomatin-deficient cryohydrocytosis (sdCHC), a rare form of stomatocytosis associated with a cold-induced cation leak, hemolytic anemia, and hepatosplenomegaly but also with cataracts, seizures, mental retardation, and movement disorder. We now show that sdCHC is associated with mutations in SLC2A1 that cause both loss of glucose transport and a cation leak, as shown by expression studies in Xenopus oocytes. On the basis of a 3-dimensional model of glut1, we propose potential mechanisms underlying the phenotypes of the 2 mutations found. We investigated the loss of stomatin during erythropoiesis and find this occurs during reticulocyte maturation and involves endocytosis. The molecular basis of the glut1DS, paroxysmal exercise-induced dyskinesia, and sdCHC phenotypes are compared and discussed.

Structure, function and significance of Rh proteins in red cells

Purpose of reviewThe present article reviews recent data concerning the structure and function of the Rh-associated glycoprotein (RhAG) and considers what can be inferred about the structure and functional significance of the D and CE polypeptides. Recent findingsThe structure of a bacterial RhAG (from Nitrosomonas europaea) has been solved and its gas channel elucidated. This information allows us to model a more accurate structure of RhD and RhCE polypeptides than has been possible hitherto. Human RhAG has been shown to act as a gas channel for CO2. SummaryElucidation of the structure of a bacterial RhAG allows us to model the structure of D and CE polypeptides more accurately than before. Results suggest that whereas RhAG has a channel for passage of neutral gases (CO2, NH3 and possibly oxygen and nitric oxide), D and CE polypeptides are unlikely to have a transport function.

Two MER2‐negative individuals with the same novel CD151 mutation and evidence for clinical significance of anti‐MER2

BACKGROUND: MER2 (RAPH1), the only antigen of the RAPH blood group system, is located on the tetraspanin CD151. Only four examples of alloanti‐MER2 are known. We report here two new examples of alloanti‐MER2, in women of Pakistani and Turkish origin, one of whom showed signs of a hemolytic transfusion reaction (HTR) after transfusion of 3 units of red cells (RBCs).

An Enlarged, Adaptable Active Site in CYP164 Family P450 Enzymes, the Sole P450 in Mycobacterium leprae

ABSTRACT CYP164 family P450 enzymes are found in only a subset of mycobacteria and include CYP164A1, which is the sole P450 found in Mycobacterium leprae, the causative agent of leprosy. This has previously led to interest in this enzyme as a potential drug target. Here we describe the first crystal structure of a CYP164 enzyme, CYP164A2 from Mycobacterium smegmatis. CYP164A2 has a distinctive, enlarged hydrophobic active site that extends above the porphyrin ring toward the access channels. Unusually, we find that CYP164A2 can simultaneously bind two econazole molecules in different regions of the enlarged active site and is accompanied by the rearrangement and ordering of the BC loop. The primary location is through a classic interaction of the azole group with the porphyrin iron. The second econazole molecule is bound to a unique site and is linked to a tetracoordinated metal ion complexed to one of the heme carboxylates and to the side chains of His 105 and His 364. All of these features are preserved in the closely homologous M. leprae CYP164A1. The computational docking of azole compounds to a homology model of CYP164A1 suggests that these compounds will form effective inhibitors and is supported by the correlation of parallel docking with experimental binding studies of CYP164A2. The binding of econazole to CYP164A2 occurs primarily through the high-spin “open” conformation of the enzyme (Kd [dissociation constant] of 0.1 μM), with binding to the low-spin “closed” form being significantly hindered (Kd of 338 μM). These studies support previous suggestions that azole derivatives may provide an effective strategy to improve the treatment of leprosy.