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The construction of peptides to mimic heterogeneous proteins such as type I collagen plays a pivotal role in deciphering their function and pathogenesis. However, progress in the field has been severely hampered by the lack of capability to create stable heterotrimers with desired functional sequences and without the effect of homotrimers. We have herein developed a set of triblock peptides that can assemble into collagen mimetic heterotrimers with desired amino acids and are free from the interference of homotrimers. The triblock peptides comprise a central collagen-like block and two oppositely charged N-/C-terminal blocks, which display inherent incompetency of homotrimer formation. The favorable electrostatic attraction between two paired triblock peptides with complementary terminal charged sequences promptly leads to stable heterotrimers with controlled chain composition. The independence of the collagen-like block from the two terminal blocks endows this system with the adaptability to incorporate desired amino acid sequences while maintaining the heterotrimer structure. The triblock peptides provide a versatile and robust tool to mimic the composition and function of heterotrimer collagen and may have great potential in the design of innovative peptides mimicking heterogeneous proteins. [ABSTRACT FROM AUTHOR]

Using automated stepwise Edman degradation of suitable overlapping peptides, the complete amino acid sequence of the 268 residue peptida α1-CB7 from calf skin collagen was determined. The preparation and ordering of the chymotryptic, tryptic and thermolytic peptides is described in the preceding paper. As shown previously for other peptides from the helical region of collagen, glycine appears in every third position and proline is present in high amount. Hydroxylation of proline to 4-hydroxyproline and lysine to hydroxylysine only occurred in the Y position of the tripeptide unit Gly-X-Y. Non-random distribution of other amino acids between the X and Y positions was also observed. [ABSTRACT FROM AUTHOR]

Sequencing of chyinotrypsin, trypsin, collagenase- and hydroxylamine-derived peptides, using the automated Edman degradation procedure, yielded the complete amino acid sequence of α2-CB4 from calf skin collagen (321 residues). Together with the data from earlier work, an uninterrupted sequence in the helical region of the α2-chain from residues 1-393 is now known. Glycine is found in every third position of the peptide. Hydroxylation of proline and lysine occurs only in the Y-position of the triplet Gly-X-Y and is not complete in every position. Some residues, such as glutamic acid, leucine, phenylalanine and arginine, are distributed non-randomly between the X and Y-positions and this non-random distribution is different in the α1 and α2-chains. Comparison of the N-terminal 393 residues from the helical region of the α1 and α2-chains revealed a nearly identical distribution of charged polar residues arginine, lysine, glutamic and aspartic acids. The distribution of the triplet Gly-Pro-Hyp is similar in both chains. The remaining residues in the α2-chain exhibit a high degree of substitutions when compared with those in the α1-chain. Approximately one in every two residues in both the X and Y-positions are substituted. [ABSTRACT FROM AUTHOR]

Collagen occurs in two major forms: fibrillar and non-fibrillar. Non-fibrillar collagens are structurally more variable and relatively ill-understood. In this work we analysed the amino acid sequence of type VI collagen, a non-fibrillar collagen that forms antiparallet dimers. A sequence motif was discovered that gives rise to systematic molecular coiling. There is a common periodicity (∼23 or 2 × 23 residues) in the charged amino acids, in the prolines and in the discontinuities in the GIy-X-Y triplets. In addition, there is a different periodicity (∼21 amino acids) in the apolar groups. The two repeats mean that the only way to simultaneously maximize both the hydrophobic and polar interactions during dimer formation is with the molecules antiparallel, overlapped by 75 nm as observed, and supercoiled. The alternating prolinerich and charge-rich patches, often together with discontinuities in the GIy-X-Y sequences, coincide with each half-turn of the supercoil, thus breaking it into segments. We have termed this structure the collagen segmented supercoil. The segmented supercoil and variants may be common aggregation motifs for the non-fibrillar collagens. [ABSTRACT FROM AUTHOR]