For hydrophobic compounds [10]. Fatty acids (FA’s) have diverse and important biological functions in cells. They are involved in protein acylation, transcription regulation, apoptosis, energy production and storage,and membrane synthesis [11,12]. They are essential key components in numerous signaling cascades involving TLR and insulin signaling as well 25033180 as inflammatory responses [12,13]. FA’s comprise approximately 30?0 of total fatty acids in animal tissues, with the majority being palmitic acid (15?5 ), followed by stearic acid (10?0 ), myristic acid (0.5? ), and lauric acid (,0.5 ) [14]. Natural receptors for FA’s include family members of the albumin and fatty acid-binding protein (FABP) family [15]. These proteins serve to 
increase the solubility of fatty acids and mediate their transport within cells. While there are many members of the FABP family with a great deal of variance in protein sequence, all members share a common ?barrel structural motif [15]. The 10stranded antiparallel ?barrel contains a hydrophobic core to which fatty acids bind. The core is capped on one end by an Nterminal helix-turn-helix motif. Inside the binding pocket, the carboxyl group is coordinated through electrostatic interactions with tyrosine and two arginine residues. The hydrocarbon tail is oriented with hydrophobic residues on one side and ordered water ML 281 biological activity molecules on the other side [16]. Multiple fatty acid binding sites have been shown for Human Serum Albumin revealing a combined contribution of electrostatic and hydrophobic forces to the binding interactions [17]. Interestingly, the carboxylate head group of the bound fatty acids are more tightly bound than their methylene tail [18]. In the current work, we have solved the crystal structures of COMPcc in complex with myristic acid (C14:0), palmitic acidBinding of Fatty Acids to COMPsulfate. order PLV-2 individual fatty acids obtained from Sigma were soaked in an equimolar ratio into the crystals for 6 hours. Palmititc acid titration experiments were performed by adding molar excess and incubation overnight. The crystals belong to spacegroup P21 and contain one molecule of the pentameric COMPcc within the asymmetric unit. To analyze the influence of different effectors (pH, ions and organic solvents) four crystal structures performing different crystallization conditions were determined (data not shown). The high resolution data sets were collected at synchrotron CLS (PX-Beamline) on a MAR research imaging plate detector. Diffraction images were processed using program suite MOSFLM [19] and the structure factors were scaled and reduced using SCALA from the CCP4 package [20]. Statistics of the merged data is given.Structure determination and refinementMolecular replacement was performed using the AMORE program of the CCP4 package [20]. A Poly-serine model of native COMPcc structure (PDB-code:1MZ9) was used as search template. Positional refinement was performed with CNS using the maximum likelihood method [21]. Five to ten percent of the reflections were excluded for use in a cross validation set. Refinement with CNS was alternated with manual electron density refitting of side-chains and terminal regions using MAIN. At this stage the individual fatty acid molecules have been fitted into a 3.0s contoured Fo-Fc difference map. To determine the favoured axial orientation of the ligands within the pentameric channel a 2u stepwise refinement (conjugated gradient minimization together with 
individual B-factor refin.For hydrophobic compounds [10]. Fatty acids (FA’s) have diverse and important biological functions in cells. They are involved in protein acylation, transcription regulation, apoptosis, energy production and storage,and membrane synthesis [11,12]. They are essential key components in numerous signaling cascades involving TLR and insulin signaling as well 25033180 as inflammatory responses [12,13]. FA’s comprise approximately 30?0 of total fatty acids in animal tissues, with the majority being palmitic acid (15?5 ), followed by stearic acid (10?0 ), myristic acid (0.5? ), and lauric acid (,0.5 ) [14]. Natural receptors for FA’s include family members of the albumin and fatty acid-binding protein (FABP) family [15]. These proteins serve to increase the solubility of fatty acids and mediate their transport within cells. While there are many members of the FABP family with a great deal of variance in protein sequence, all members share a common ?barrel structural motif [15]. The 10stranded antiparallel ?barrel contains a hydrophobic core to which fatty acids bind. The core is capped on one end by an Nterminal helix-turn-helix motif. Inside the binding pocket, the carboxyl group is coordinated through electrostatic interactions with tyrosine and two arginine residues. The hydrocarbon tail is oriented with hydrophobic residues on one side and ordered water molecules on the other side [16]. Multiple fatty acid binding sites have been shown for Human Serum Albumin revealing a combined contribution of electrostatic and hydrophobic forces to the binding interactions [17]. Interestingly, the carboxylate head group of the bound fatty acids are more tightly bound than their methylene tail [18]. In the current work, we have solved the crystal structures of COMPcc in complex with myristic acid (C14:0), palmitic acidBinding of Fatty Acids to COMPsulfate. Individual fatty acids obtained from Sigma were soaked in an equimolar ratio into the crystals for 6 hours. Palmititc acid titration experiments were performed by adding molar excess and incubation overnight. The crystals belong to spacegroup P21 and contain one molecule of the pentameric COMPcc within the asymmetric unit. To analyze the influence of different effectors (pH, ions and organic solvents) four crystal structures performing different crystallization conditions were determined (data not shown). The high resolution data sets were collected at synchrotron CLS (PX-Beamline) on a MAR research imaging plate detector. Diffraction images were processed using program suite MOSFLM [19] and the structure factors were scaled and reduced using SCALA from the CCP4 package [20]. Statistics of the merged data is given.Structure determination and refinementMolecular replacement was performed using the AMORE program of the CCP4 package [20]. A Poly-serine model of native COMPcc structure (PDB-code:1MZ9) was used as search template. Positional refinement was performed with CNS using the maximum likelihood method [21]. Five to ten percent of the reflections were excluded for use in a cross validation set. Refinement with CNS was alternated with manual electron density refitting of side-chains and terminal regions using MAIN. At this stage the individual fatty acid molecules have been fitted into a 3.0s contoured Fo-Fc difference map. To determine the favoured axial orientation of the ligands within the pentameric channel a 2u stepwise refinement (conjugated gradient minimization together with individual B-factor refin.