Ered (data not shown). Based upon this observation we propose that the region Leu37 to Leu51 form the core hydrophobic fatty acid binding region. A significant structural difference was observed in the binary COMPcc-oleic acid complex. Oleic acid (C18:1), whose aliphatic tail has a single cis-Lecirelin biological activity double bond, is held fixed to Leu44 at the cisdouble bond kink, while the rest of the aliphatic tail remains LY-2409021 site highly disordered. The opening of the unligated COMPcc channel has ?been determined to be of maximal width (,6 A) at position Val47. This region, therefore, serves to accommodate the cis-configured double bond of oleic acid (Fig. 1A) [6]. The sp2-hybridized double bond between C9-C10 of oleic acid is thus tightly fitted into a hydrophobic ring of the b-branched side chains of Val47, which is a d residue in the heptad repeat pattern of COMPcc. Oleic acids C11 methylene, that immediately follows the double bond, forms van der Waals contacts with three of the five Leu44 side chains in its vicinity.CPA Kd??and A OMPcc A{COMPccFA Kd??In these experiments, the concentration of COMPcc is kept low, both relative to KdCPA and relative to CPA and the concentration of CPA is also kept significantly lower than KdCPA (the initial concentration of COMPcc is ,0.1 mM and CPA is equal to 0.4 mM). In the case where there is no FA added the concentrations are [COMPcc] = [COMPcc]0 and [CPA]<[CPA]0 = 0.4 mM. In this case the concentration of the CPACOMPcc complex will be equal to: OMPcc{CPA0 PA0 { OMPcc0 PA0 OMPcc0 CPA Kd ??At A A1=2 ,the concentration of the COMPcc-CPA complex is equal to one half the initial: OMPcc{CPA A1 0:=PA0 OMPcc0 CPA Kd??Writing a mass balance for COMPcc we obtain: OMPcc0 OMPccz OMPcc{CPAz OMPcc{FA When A A1=2 : PA0 CPA Kd 1= 2 A1= 1z FA 2 Kd 1{??Palmitic acid ?inside and outside of the pentameric channel system??The structural studies on palmitic acid (C16:0) in complex with COMPcc reveal the presence of two ligand molecules at separate sites (Figure 2). The fatty acid inside the COMPcc channel adopts ?a linear, elongated conformation with a total length of ,19 A (Figure 2A). With its terminal methylene groups, C15 16, the palmitic acid reaches into the cavity between Leu37 (position a inBinding of Fatty Acids to COMPTable 1. Data collection and refinement data.Data collection Fatty acid Pdb-code ?Resolution range (A) Unique reflections Completeness Redundancy Rsym1 ?Cell dimensions (A,u) A B C b Refinement Rfactor2 ( ), no sigma cutoff RfreeC14 3V2N20.6-1.8 (1.9-1.8) 17542 94.9 (94.3) 2.0 10.1 (31.8)C16 3V2Q24-2.2 (2.32-2.2) 9799 99.1 (98.7) 4.4 8.1 (29.6)C18 3V2P29.4-1.87 (1.99-1.87) 15795 99.3 (95.7) 4.0 7.4 (28.9)C18:1 3V2R29.4-2.75 (2.92-2.75) 4761 92.6 (93.0) 2.9 8.3 (32.4)38.35 49.39 54.82 103.38.7 48.5 53.3 103.37.9 48.9 53.9 104.37.86 49.11 54.25 104.21.2 (26) 27.6 (33)20.8 (23.0) 27.5 (31.1)20.7 (28.5) 25.5 (35.7)20.1 (31.3) 27.5 (36.3)( ), no sigma cutoff?Average B factors (A2) Protein/Water/Ligands ?Bond length (A)3 Bond angles (u)3 Ramachandran plot4 26.3/44.3/35.2 0.005 0.9 96.7/2.4/0.5/0.5 48.9/66.1/45.8 0.006 1.0 95.7/3.3/0/1 29.6/39.3/38.5 0.005 0.9 97.6/1.5/0/1.0 41.6/38.5/37.1 0.008 1.1 93.8/5.2/0.5/0.Values for the highest resolution shells are in parentheses. 1 Rsym = 100 * SI2,I.|/SI. 2 Rfactor = S||Fobs|2|Fcalc|/S|Fobs|. 3 Root-mean-square error. 4 ?Percentage of residues in most favoured/additional allowed/generously allowed and disallowed regions. All datasets were measured at a wavelen.Ered (data not shown). Based upon this observation we propose that the region Leu37 to Leu51 form the core hydrophobic fatty acid binding region. A significant structural difference was observed in the binary COMPcc-oleic acid complex. Oleic acid (C18:1), whose aliphatic tail has a single cis-double bond, is held fixed to Leu44 at the cisdouble bond kink, while the rest of the aliphatic tail remains highly disordered. The opening of the unligated COMPcc channel has ?been determined to be of maximal width (,6 A) at position Val47. This region, therefore, serves to accommodate the cis-configured double bond of oleic acid (Fig. 1A) [6]. The sp2-hybridized double bond between C9-C10 of oleic acid is thus tightly fitted into a hydrophobic ring of the b-branched side chains of Val47, which is a d residue in the heptad repeat pattern of COMPcc. Oleic acids C11 methylene, that immediately follows the double bond, forms van der Waals contacts with three of the five Leu44 side chains in its vicinity.CPA Kd??and A OMPcc A{COMPccFA Kd??In these experiments, the concentration of COMPcc is kept low, both relative to KdCPA and relative to CPA and the concentration of CPA is also kept significantly lower than KdCPA (the initial concentration of COMPcc is ,0.1 mM and CPA is equal to 0.4 mM). In the case where there is no FA added the concentrations are [COMPcc] = [COMPcc]0 and [CPA]<[CPA]0 = 0.4 mM. In this case the concentration of the CPACOMPcc complex will be equal to: OMPcc{CPA0 PA0 { OMPcc0 PA0 OMPcc0 CPA Kd ??At A A1=2 ,the concentration of the COMPcc-CPA complex is equal to one half the initial: OMPcc{CPA A1 0:=PA0 OMPcc0 CPA Kd??Writing a mass balance for COMPcc we obtain: OMPcc0 OMPccz OMPcc{CPAz OMPcc{FA When A A1=2 : PA0 CPA Kd 1= 2 A1= 1z FA 2 Kd 1{??Palmitic acid ?inside and outside of the pentameric channel system??The structural studies on palmitic acid (C16:0) in complex with COMPcc reveal the presence of two ligand molecules at separate sites (Figure 2). The fatty acid inside the COMPcc channel adopts ?a linear, elongated conformation with a total length of ,19 A (Figure 2A). With its terminal methylene groups, C15 16, the palmitic acid reaches into the cavity between Leu37 (position a inBinding of Fatty Acids to COMPTable 1. Data collection and refinement data.Data collection Fatty acid Pdb-code ?Resolution range (A) Unique reflections Completeness Redundancy Rsym1 ?Cell dimensions (A,u) A B C b Refinement Rfactor2 ( ), no sigma cutoff RfreeC14 3V2N20.6-1.8 (1.9-1.8) 17542 94.9 (94.3) 2.0 10.1 (31.8)C16 3V2Q24-2.2 (2.32-2.2) 9799 99.1 (98.7) 4.4 8.1 (29.6)C18 3V2P29.4-1.87 (1.99-1.87) 15795 99.3 (95.7) 4.0 7.4 (28.9)C18:1 3V2R29.4-2.75 (2.92-2.75) 4761 92.6 (93.0) 2.9 8.3 (32.4)38.35 49.39 54.82 103.38.7 48.5 53.3 103.37.9 48.9 53.9 104.37.86 49.11 54.25 104.21.2 (26) 27.6 (33)20.8 (23.0) 27.5 (31.1)20.7 (28.5) 25.5 (35.7)20.1 (31.3) 27.5 (36.3)( ), no sigma cutoff?Average B factors (A2) Protein/Water/Ligands ?Bond length (A)3 Bond angles (u)3 Ramachandran plot4 26.3/44.3/35.2 0.005 0.9 96.7/2.4/0.5/0.5 48.9/66.1/45.8 0.006 1.0 95.7/3.3/0/1 29.6/39.3/38.5 0.005 0.9 97.6/1.5/0/1.0 41.6/38.5/37.1 0.008 1.1 93.8/5.2/0.5/0.Values for the highest resolution shells are in parentheses. 1 Rsym = 100 * SI2,I.|/SI. 2 Rfactor = S||Fobs|2|Fcalc|/S|Fobs|. 3 Root-mean-square error. 4 ?Percentage of residues in most favoured/additional allowed/generously allowed and disallowed regions. All datasets were measured at a wavelen.

Ered (data not shown). Based upon this observation we propose that

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