Structure of human ORP3 ORD reveals conservation of a key function and ligand specificity in OSBP-related proteins.

Human ORP3 belongs to the oxysterol-binding protein (OSBP) family of lipid transfer proteins and is involved in lipid trafficking and cell signaling. ORP3 localizes to the ER-PM interfaces and is implicated in lipid transport and focal adhesion dynamics. Here, we report the 2.6-2.7 Å structures of the ORD (OSBP-related domain) of human ORP3 in apo-form and in complex with phosphatidylinositol 4-phosphate. The ORP3 ORD displays a helix grip ß-barrel fold with a deep hydrophobic pocket which is conserved in the OSBP gene family. ORP3 binds PI(4)P by the residues around tunnel entrance and in the hydrophobic pocket, whereas it lacks sterol binding due to the narrow hydrophobic tunnel. The heterologous expression of the ORDs of human ORP3 or OSBP1 rescued the lethality of seven ORP (yeast OSH1-OSH7) knockout in yeast. In contrast, the PI(4)P-binding site mutant of ORP3 did not complement the OSH knockout cells. The N-terminal PH domain and FFAT motif of ORP3 are involved in protein targeting but are not essential in yeast complementation. This observation suggests that the essential function conserved in the ORPs of yeast and human is mediated by PI(4)P-binding of the ORD domain. This study suggests that the non-vesicular PI(4)P transport is a conserved function of all ORPs in eukaryotes.

A fatty acid-binding protein of Streptococcus pneumoniae facilitates the acquisition of host polyunsaturated fatty acids.

Streptococcus pneumoniae is responsible for the majority of pneumonia, motivating ongoing searches for insights into its physiology that could enable new treatments. S. pneumoniae responds to exogenous fatty acids by suppressing its de novo biosynthetic pathway and exclusively utilizing extracellular fatty acids for membrane phospholipid synthesis. The first step in exogenous fatty acid assimilation is phosphorylation by fatty acid kinase (FakA), whereas bound by a fatty acid-binding protein (FakB). Staphylococcus aureus has two binding proteins, whereas S. pneumoniae expresses three. The functions of these binding proteins were not clear. We determined the SpFakB1- and SpFakB2-binding proteins were bioinformatically related to the two binding proteins of Staphylococcus aureus, and biochemical and X-ray crystallographic analysis showed that SpFakB1 selectively bound saturates, whereas SpFakB2 allows the activation of monounsaturates akin to their S. aureus counterparts. The distinct SpFakB3 enables the utilization of polyunsaturates. The SpFakB3 crystal structure in complex with linoleic acid reveals an expanded fatty acid-binding pocket within the hydrophobic interior of SpFakB3 that explains its ability to accommodate multiple cis double bonds. SpFakB3 also utilizes a different hydrogen bond network than other FakBs to anchor the fatty acid carbonyl and stabilize the protein. S. pneumoniae strain JMG1 (ΔfakB3) was deficient in incorporation of linoleate from human serum verifying the role of FakB3 in this process. Thus, the multiple FakBs of S. pneumoniae permit the utilization of the entire spectrum of mammalian fatty acid structures to construct its membrane.

Structural analysis uncovers lipid-binding properties of Notch ligands.

The Notch pathway is a core cell-cell signaling system in metazoan organisms with key roles in cell-fate determination, stem cell maintenance, immune system activation, and angiogenesis. Signals are initiated by extracellular interactions of the Notch receptor with Delta/Serrate/Lag-2 (DSL) ligands, whose structure is highly conserved throughout evolution. To date, no structure or activity has been associated with the extreme N termini of the ligands, even though numerous mutations in this region of Jagged-1 ligand lead to human disease. Here, we demonstrate that the N terminus of human Jagged-1 is a C2 phospholipid recognition domain that binds phospholipid bilayers in a calcium-dependent fashion. Furthermore, we show that this activity is shared by a member of the other class of Notch ligands, human Delta-like-1, and the evolutionary distant Drosophila Serrate. Targeted mutagenesis of Jagged-1 C2 domain residues implicated in calcium-dependent phospholipid binding leaves Notch interactions intact but can reduce Notch activation. These results reveal an important and previously unsuspected role for phospholipid recognition in control of this key signaling system.

Análisis estructural y funcional de proteínas solubles que unen lípidos de parásitos helmintos / Structural and functional analysis of soluble lipid binding proteins from parasitic helminths / Análise estrutural e funcional de proteínas solúveis que ligam lipídios de parasitas helmintos

Los parásitos helmintos producen y secretan una gran variedad de proteínas que unen lípidos (LBPs, del inglés lipid binding proteins) que podrían participar en la obtención de nutrientes tales como ácidos grasos y colesterol desde el hospedador. Asimismo, se postula que las LBPs podrían intervenir en la regulación de la respuesta inmune del hospedador. Conocer más acerca de las estructuras de estas proteínas, así como de sus interacciones con ligandos y membranas, es claramente pertinente para comprender las interacciones parásito-hospedador que ellas pudieran mediar. Por otra parte, dichos estudios permitirán profundizar en el conocimiento de los mecanismos de infección helmíntica y en el papel que estas proteínas juegan en la biología de los helmintos en general. Asimismo, esta información podría contribuir al establecimiento de medidas terapéuticas y de prevención de las enfermedades causadas por estos parásitos.

Helminth parasites produce and secrete a great variety of lipid binding proteins (LBPs) that may participate in the acquisition of nutrients such as fatty acids and cholesterol from their host. It is also postulated that LBPs might interfere in the regulation of the host's immune response. Knowing more about the structure of these proteins as well as their interactions with ligands and membranes is important in order to understand the host-parasite interaction that they could mediate. On the other hand, these studies will contribute to obtain further knowledge about the mechanisms of helminth infection and the role that these proteins play in helminth biology. Moreover, this information would be useful to set new therapeutic and prevention measures for the diseases caused by these parasites.

Os parasitas helmintos produzem e secretam uma grande variedade de proteínas que ligam lipídios, LBPs (Lipid Binding Proteins, por sua sigla em inglês), que poderiam estar envolvidas na obtenção de nutrientes tais como ácidos graxos e colesterol a partir do hospedeiro. Do mesmo modo, é postulado que as LBPs poderiam intervir na regulação da resposta imune do hospedeiro. Saber mais sobre as estruturas dessas proteínas, bem como sobre as suas interações com ligantes e membranas é claramente pertinente para compreender as interações parasita-hospedeiro que elas pudessem mediar. Além disso, estes estudos irão permitir um melhor entendimento dos mecanismos de infecção helmíntica e o papel que estas proteínas desempenham na biologia de helmintos em geral. Também, essa informação poderia ajudar a estabelecer medidas terapêuticas e de prevenção das doenças provocadas por esses parasitas.