Folding and conformational consequences of glycine to alanine replacements at different positions in a collagen model peptide.
The collagen model peptide T1-892 includes a C-terminal nucleation domain, (Gly-Pro-Hyp)(4), and an N-terminal (Gly-X-Y)(6) sequence taken from type I collagen. In osteogenesis imperfecta (OI) and other collagen diseases, single base mutations often convert one Gly to a larger residue, and T1-892 homologues modeling such mutations were synthesized with Gly to Ala substitutions in either the (Gly-Pro-Hyp)(4) domain, Gly25Ala, or the (Gly-X-Y)(6) domain, Gly10Ala. CD and NMR studies show the Gly10Ala peptide forms a normal triple-helix at the C-terminal end and propagates from the C- to the N-terminus until the Gly --> Ala substitution is encountered. At this point, triple-helix folding is terminated and cannot be reinitiated, leaving a nonhelical N-terminus. A decreased thermal stability is observed as a result of the shorter length of the triple-helix. In contrast, introduction of the Gly to Ala replacement at position 25, in the nucleation domain, shifts the monomer/trimer equilibrium toward the monomer form. The increased monomer and lower trimer populations are reflected in the dramatic decrease in triple-helix content and stability. Unlike the Ala replacement at position 10, the Ala substitution in the (Gly-Pro-Hyp)(4) region can still be incorporated into a triple-helix, but at a greatly decreased rate of folding, since the original efficient nucleation site is no longer operative. The specific consequences of Gly to Ala replacements in two distinctive sequences in this triple-helical peptide may help clarify the variability in OI clinical severity resulting from mutations at different sites along type I collagen chains.
Bhate
Manjiri
M
Department of Biochemistry, UMDNJ-Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, New Jersey 08854, USA.
Wang
Xin
X
Baum
Jean
J
Brodsky
Barbara
B
D000409:Alanine / Q000737:chemistry*; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D002942:Circular Dichroism; D024042:Collagen Type I / Q000138:chemical synthesis*; D005998:Glycine / Q000737:chemistry*; D007098:Imino Acids / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010446:Peptide Fragments / Q000138:chemical synthesis*; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013816:Thermodynamics
D024042:Collagen Type I; D007098:Imino Acids; D010446:Peptide Fragments; D000409:Alanine; D005998:Glycine