Figure 1

(A) The consensus sequence for mammalian collagen type I arranged by D period, the expected arrangement in in vivo collagen fibrils⁴⁴ showing the distribution of charged residues along the sequence. The collagen molecule consists of three peptide chains, two α1 and one α2 chain, each staggered by one residue with respect to each other and twisted into a triple helix for the majority of their length (stagger not shown because it is unknown whether the heterochain, a2, is in the leading, middle or trailing position within the triple helix). The schematic corresponds to the repeat unit cell in a collagen fibril. This arrangement leads to the so-called overlap zone, where all five D periods overlap and the gap zone where the short D5 period leads to a gap or hole in the fibrillar structure. Note that only the triple helical region of the molecule is shown and that the non-helical N- and C-terminal telopeptide sequences are not shown. The charged amino acids are highlighted in red (negatively charged residues) and blue (positively charged residues). The regions enclosed in rectangular boxes indicate collagen sub-bands as determined by TEM⁴⁴. These regions contain an abundance of charged residues, both positively and negatively charged (note that the schematic does not represent the exact alignment of charges because the chain stagger within the triple helix is not included here and because the triple helix does not have constant pitch over its length). (B) 2D representation of the collagen type I fibril structure determined from x-ray diffraction analysis (3HR2) for one D period with N- and C-terminal telopeptides included⁵⁷, showing the spatial distribution of charged residues. Charged residues highlighted as in (A). Note that only Cα atoms are shown and that the spheres representing them are not indicating van der Waals radii.