title: Stability junction at a common mutation site in the collagenous domain of the mannose binding lectin.
abstract: Missense mutations in the collagen triple-helix that replace one of the required Gly residues in the (Gly-Xaa-Yaa)(n)() repeating sequence have been implicated in various disorders. Although most hereditary collagen disorders are rare, a common occurrence of a Gly replacement mutation is found in the collagenous domain of mannose binding lectin (MBL). A Gly --> Asp mutation at position 54 in MBL is found at a frequency as high as 30% in certain populations and leads to increased susceptibility to infections. The structural and energetic consequences of this mutation are investigated by comparing a triple-helical peptide containing the N-terminal Gly-X-Y units of MBL with the homologous peptide containing the Gly to Asp replacement. The mutation leads to a loss of triple-helix content but only a small decrease in the stability of the triple-helix (DeltaT(m) approximately 2 degrees C) and no change in the calorimetric enthalpy. NMR studies on specifically labeled residues indicate the portion of the peptide C-terminal to residue 54 is in a highly ordered triple-helix in both peptides, while residues N-terminal to the mutation site have a weak triple-helical signal in the parent peptide and are completely disordered in the mutant peptide. These results suggest that the N-terminal triplet residues are contributing little to the stability of this peptide, a hypothesis confirmed by the stability and enthalpy of shorter peptides containing only the region C-terminal to the mutation site. The Gly to Asp replacement at position 54 in MBL occurs at the boundary of a highly stable triple-helix region and a very unstable sequence. The junctional position of this mutation minimizes its destabilizing effect, in contrast with the significant destabilization seen for Gly replacements in peptides modeling collagen diseases.
authors.affiliation: Department of Biochemistry, UMDNJ-Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA.
authors.forename: Angela
authors.initials: A
authors.lastname: Mohs
authors.forename: Yingjie
authors.initials: Y
authors.lastname: Li
authors.forename: Ellen
authors.initials: E
authors.lastname: Doss-Pepe
authors.forename: Jean
authors.initials: J
authors.lastname: Baum
authors.forename: Barbara
authors.initials: B
authors.lastname: Brodsky
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D003094:Collagen / Q000138:chemical synthesis / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D006860:Hydrogen Bonding; D037601:Mannose-Binding Lectin / Q000138:chemical synthesis / Q000235:genetics* / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D019906:Nuclear Magnetic Resonance, Biomolecular; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D017434:Protein Structure, Tertiary / Q000235:genetics; D013816:Thermodynamics
chemical_list: D037601:Mannose-Binding Lectin; D010446:Peptide Fragments; D003094:Collagen