Collagen Alpha 1(1)

The Alpha 1(1) subunit of collagen is the largest protein represented in this set of pieces and is also the basis for the longest piece of music. Collagen is a major component of the connective tissue meshwork that runs through animal bodies. It is secreted by connective tissue cells. The fibril consists of three polypeptide chains wound around one another to form a strong triple helix. The Alpha 1(1) subunit is one of the three chains of type I collagen; the sequence represented here is the human sequence.

Collagen is first synthesized as a large precursor protein containing over 1400 amino acids. Only about 1000 of these are present in a mature collagen fibril. However, other parts of the protein are essential for its secretion from the cell and for forming the triple helix. A short "signal" sequence moves the protein across the membranes that will form secretion vesicles. On either side of the helix-forming region are two sections that interact with similar regions of two other collagen chains to align the three chains for formation of the triple helix. After the helix has been secreted by the cell, these alignment sequences are removed from the protein.

The collagen precursor then has four natural sections: signal-alignment-helix-alignment. Each segment has a characteristic structure. The signal sequence is rich in hydrophobic amino acids, which dissolve easily in cell membranes. The first of the two alignment sections can actually be divided into three segments: the first is rich in the amino acid cysteine, which can form cross-links between adjacent protein chains. The second is rich in the amino acid glycine, which occupies every third position to set up a rhythmic preview of the long repetitve helix-forming section, in which glycine is also repeated every three amino acids. The third segment is neither cysteine nor glycine rich. The second alignment section, unlike the first, does not contain a reiterated sequence.

The helix forming region is composed predominantly of three amino acids: glycine, which occurs in every third position throughout the long sequence; proline, which frequently follows glycine in this segment, and alanine. The regular reiteration of glycine through hundreds of amino acids sets up a hypnotic rhythm, within which amino acid triplets fall in patterns that become familiar, but are not quite predictable. for example ...GPPGPSGNAGPPGPPGPAGKEGGKGPR.... Glycine is the smallest of the amino acids and in the collagen triple helix, the glycines of adjacent polypeptide chains are packed close together.

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Collagen Alpha 1(1)

! = end of signal sequence
{ } = alignment segments
[ ] = repeptitive sequence within the first alignment segment
( ) = helix-forming region




Link to the Music: Collagen

Notes on the Music:

This piece was composed by John Dunn for the Life Music CD. The piece is divided into five segments, which can be heard as five movements. The first includes both the signal sequence and the cysteine-rich region of the first alignment segment. The second is the helix-foreshadowing section of the alignment segment. The third is the last part of the alignment segment. The fourth is the helix-forming region. the fifth is the second alignment segment. These can be heard as different landscapes encountered during a journey through this long protein, which itself forms a sort of highway extending throughout the organism.