Differential Ligand Binding Specificities of the Pulmonary Collectins Are Determined by the Conformational Freedom of a Surface Loop.

Lung surfactant proteins (SPs) play critical roles in surfactant function and innate immunity. SP-A and SP-D, members of the collectin family of C-type lectins, exhibit distinct ligand specificities, effects on surfactant structure, and host defense functions despite extensive structural homology. SP-A binds to dipalmitoylphosphatidylcholine (DPPC), the major surfactant lipid component, but not phosphatidylinositol (PI), whereas SP-D shows the opposite preference.

IcmQ in the Type 4b secretion system contains an NAD+ binding domain.

A Type 4b secretion system (T4bSS) is required for Legionella growth in alveolar macrophages. IcmQ associates with IcmR, binds to membranes, and has a critical role in the T4bSS. We have now solved a crystal structure of IcmR-IcmQ to further our understanding of this complex.

Mutational analysis of the multiple-antibiotic resistance regulator MarR reveals a ligand binding pocket at the interface between the dimerization and DNA binding domains.

The Escherichia coli regulator MarR represses the multiple-antibiotic resistance operon marRAB and responds to phenolic compounds, including sodium salicylate, which inhibit its activity. Crystals obtained in the presence of a high concentration of salicylate indicated two possible salicylate sites, SAL-A and SAL-B. However, it was unclear whether these sites were physiologically significant or were simply a result of the crystallization conditions.

A unique sugar-binding site mediates the distinct anti-influenza activity of pig surfactant protein D.

Pigs can act as intermediate hosts by which reassorted influenza A virus (IAV) strains can be transmitted to humans and cause pandemic influenza outbreaks. The innate host defense component surfactant protein D (SP-D) interacts with glycans on the hemagglutinin of IAV and contributes to protection against IAV infection in mammals. This study shows that a recombinant trimeric neck lectin fragment derived from porcine SP-D (pSP-D) exhibits profound inhibitory activity against IAV, in contrast to comparable fragments derived from human SP-D.

Crystal structure and function of human nucleoplasmin (npm2): a histone chaperone in oocytes and embryos.

Human Npm2 is an ortholog of Xenopus nucleoplasmin (Np), a chaperone that binds histones. We have determined the crystal structure of a truncated Npm2-core at 1.9 Å resolution and show that the N-terminal domains of Npm2 and Np form similar pentamers.

Crystallographic complexes of surfactant protein A and carbohydrates reveal ligand-induced conformational change.

Surfactant protein A (SP-A), a C-type lectin, plays an important role in innate lung host defense against inhaled pathogens. Crystallographic SP-A·ligand complexes have not been reported to date, limiting available molecular information about SP-A interactions with microbial surface components. This study describes crystal structures of calcium-dependent complexes of the C-terminal neck and carbohydrate recognition domain of SP-A with d-mannose, D-α-methylmannose, and glycerol, which represent subdomains of glycans on pathogen surfaces.

Review: Structural determinants of pattern recognition by lung collectins.

Host defense roles for the lung collectins, surfactant protein A (SP-A) and surfactant protein D (SP-D), were first suspected in the 1980s when molecular characterization revealed their sequence homology to the acute phase reactant of serum, mannose-binding lectin. Surfactant protein A and SP-D have since been shown to play diverse and important roles in innate immunity and pulmonary homeostasis. Their location in surfactant ideally positions them to interact with air-space pathogens.

Modulation of Bacillus thuringiensis phosphatidylinositol-specific phospholipase C activity by mutations in the putative dimerization interface.

Cleavage of phosphatidylinositol (PI) to inositol 1,2-(cyclic)-phosphate (cIP) and cIP hydrolysis to inositol 1-phosphate by Bacillus thuringiensis phosphatidylinositol-specific phospholipase C are activated by the enzyme binding to phosphatidylcholine (PC) surfaces. Part of this reflects improved binding of the protein to interfaces. However, crystallographic analysis of an interfacially impaired phosphatidylinositol-specific phospholipase (W47A/W242A) suggested protein dimerization might occur on the membrane.

Structure and function of interacting IcmR-IcmQ domains from a type IVb secretion system in Legionella pneumophila.

During infection, Legionella pneumophila creates a replication vacuole within eukaryotic cells and this requires a Type IVb secretion system (T4bSS). IcmQ plays a critical role in the translocase and associates with IcmR. In this paper, we show that the N-terminal domain of IcmQ (Qn) mediates self-dimerization, whereas the C-terminal domain with a basic linker promotes membrane association.

Crystal structure of lactadherin C2 domain at 1.7A resolution with mutational and computational analyses of its membrane-binding motif.

Lactadherin is a phosphatidyl-L-serine (Ptd-L-Ser)-binding protein that decorates membranes of milk fat globules. The major Ptd-l-Ser binding function of lactadherin has been localized to its C2 domain, which shares homology with the C2 domains of blood coagulation factor VIII and factor V. Correlating with this homology, purified lactadherin competes efficiently with factors VIII and V for Ptd-L-Ser binding sites, functioning as a potent anticoagulant.

Dimer structure of an interfacially impaired phosphatidylinositol-specific phospholipase C.

The crystal structure of the W47A/W242A mutant of phosphatidylinositol-specific phospholipase C (PI-PLC) from Bacillus thuringiensis has been solved to 1.8A resolution. The W47A/W242A mutant is an interfacially challenged enzyme, and it has been proposed that one or both tryptophan side chains serve as membrane interfacial anchors (Feng, J.

Crystallographic analysis of calcium-dependent heparin binding to annexin A2.

Annexin A2 and heparin bind to one another with high affinity and in a calcium-dependent manner, an interaction that may play a role in mediating fibrinolysis. In this study, three heparin-derived oligosaccharides of different lengths were co-crystallized with annexin A2 to elucidate the structural basis of the interaction. Crystal structures were obtained at high resolution for uncomplexed annexin A2 and three complexes of heparin oligosaccharides bound to annexin A2.

High-resolution crystal structures of villin headpiece and mutants with reduced F-actin binding activity.

Villin-type headpiece domains are approximately 70 amino acid modular motifs found at the C terminus of a variety of actin cytoskeleton-associated proteins. The headpiece domain of villin, a protein found in the actin bundles of the brush border epithelium, is of interest both as a compact F-actin binding domain and as a model folded protein. We have determined the high-resolution crystal structures of chicken villin headpiece (HP67) at 1.

Purification, crystallization and preliminary X-ray analysis of the N-terminal domain of NO38, a nucleolar protein from Xenopus laevis.

NO38 is a multidomain protein that belongs to the nucleoplasmin (Np) family. Previous studies have suggested that acidic chaperones such as Np may function as histone-storage platforms. Here, the purification and crystallization of the N-terminal domain of NO38 in two crystal forms is reported.

The structure and function of Xenopus NO38-core, a histone chaperone in the nucleolus.

Xenopus NO38 is an abundant nucleolar chaperone and a member of the nucleoplasmin (Np) family. Here, we report high-resolution crystal structures of the N-terminal domain of NO38, as a pentamer and a decamer. As expected, NO38 shares the Np family fold.

Crystal structure of trimeric carbohydrate recognition and neck domains of surfactant protein A.

Surfactant protein A (SP-A), one of four proteins associated with pulmonary surfactant, binds with high affinity to alveolar phospholipid membranes, positioning the protein at the first line of defense against inhaled pathogens. SP-A exhibits both calcium-dependent carbohydrate binding, a characteristic of the collectin family, and specific interactions with lipid membrane components. The crystal structure of the trimeric carbohydrate recognition domain and neck domain of SP-A was solved to 2.

Unexpected similarity in regulation between an archaeal inositol monophosphatase/fructose bisphosphatase and chloroplast fructose bisphosphatase.

Hyperthermophilic archaea have an unusual phosphatase that exhibits activity toward both inositol-1-phosphate and fructose-1,6-bisphosphate, activities carried out by separate gene products in eukaryotes and bacteria. The structures of phosphatases from Archaeoglobus fulgidus (AF2372) and Methanococcus jannaschii (MJ0109), both anaerobic organisms, resemble the dimeric unit of the tetrameric pig kidney fructose bisphosphatase (FBPase). A striking feature of AF2372, but not of MJ0109, is that the sulfhydryl groups of two cysteines, Cys150 and Cys186, are in close proximity (4 A).

The crystal structure of Drosophila NLP-core provides insight into pentamer formation and histone binding.

The nucleoplasmin-like protein from Drosophila (dNLP) functions as a chaperone for core histones and may remodel chromatin in embryos. We now report the crystal structure of a dNLP-core pentamer at 1.5 A resolution.

Interfacial basic cluster in annexin V couples phospholipid binding and trimer formation on membrane surfaces.

Annexin V is an abundant eukaryotic protein that binds phospholipid membranes in a Ca(2+)-dependent manner. In the present studies, site-directed mutagenesis was combined with x-ray crystallography and solution liposome binding assays to probe the functional role of a cluster of interfacial basic residues in annexin V. Four mutants were investigated: R23E, K27E, R61E, and R149E.

Crystal structure of the complex between actin and human vitamin D-binding protein at 2.5 A resolution.

A high-affinity complex formed between G-actin and plasma vitamin D-binding protein (DBP) is believed to form part of a scavenging system in the plasma for removing actin released from damaged cells. In the study presented here, we describe the crystal structure of the complex between actin and human vitamin D-binding protein at 2.5 A resolution.

Biochemical and preliminary crystallographic characterization of the vitamin D sterol- and actin-binding by human vitamin D-binding protein.

Vitamin D-binding protein (DBP), a multi-functional serum glycoprotein, has a triple-domain modular structure. Mutation of Trp145 (in Domain I) to Ser decreased 25-OH-D(3)-binding by 80%. Furthermore, recombinant Domain I (1-203) and Domain I + II (1-330) showed specific and strong binding for 25-OH-D(3), but Domain III (375-427) did not, suggesting that only Domains I and II might be required for vitamin D sterol-binding.

Crystal structure of a dual activity IMPase/FBPase (AF2372) from Archaeoglobus fulgidus. The story of a mobile loop.

Several hyperthermophilic organisms contain an unusual phosphatase that has dual activity toward inositol monophosphates and fructose 1,6-bisphosphate. The structure of the second member of this family, an FBPase/IMPase from Archaeoglobus fulgidus (AF2372), has been solved. This enzyme shares many kinetic and structural similarities with that of a previously solved enzyme from Methanococcus jannaschii (MJ0109).