Amino acid sequence of the N-terminal aggregation and cross-linking region (7S domain) of the alpha1 (IV) chain of human basement membrane collagen

Abstract

The amino acid sequence of the 216-residue-long N-terminal aggregation and cross-linking 7s domain of the a1 (IV) chain of human placental basement membrane collagen is presented. The N terminus of the a1 (IV) chain starts with a non-triple-helical region, which is at least 15 residues long and contains four cysteine and two lysine residues as putative cross-linking sites. This segement is followed by a 120-residue-long triple helical region, which contains the unusual occurrence of a cysteine residue in the Xaa position of a Gly-Xaa-Yaa triplet. Since individual molecules in the 7s domain are associated in an antiparallel manner, this cysteine probably aligns with one of the four cysteines in the amino-terminal end of an adjacent molecule, forming an intermolecular disulfide bridge. The length of the overlap of two adjacent molecules is estimated to be about 110 residues. The triple helix adjacent to the overlap zone is interrupted by a 10-residue-long non-helical area, which is probably responsible for the flexible region of the molecules in the neighbourhood of the overlap zone observed in the electron microscope. The mode of aggregation of the 7s domain, the formation of intermolecular cross-links as well as the relatively high stability of this region against proteolytic attack are discussed in the light of the elucidated amino acid sequence.Type IV collagen is present in basement membranes in the form of a flexible meshwork, which acts as a scaffold to support other components and bestows some degree of mechanical strength to the matrix. Type 1V collagen molecules are 400 nm in length [I -31 and contain two different polypeptide chains designated a1 (IV) and a2(1V), each of which is approximately 1700 amino acids long [4, 51. The meshwork is formed by like ends of the molecules being associated by reducible and non-reducible cross-links [I].The central part of the molecule is an approximately 1400-residue-long triple helix. About two-thirds of the human a3 chain in this region has been sequenced [8]. This and other sequence studies on mouse [6] and bovine [7] type IV collagens indicate that the repetitive triplet Gly-Xaa-Yaa structure, characteristic of all other collagen types, is frequently interrupted. These short non-triplet sequences bestow a degree of flexibility on the molecule and also presumably the macromolecular network [9].The carboxy terminus of the molecule is a globular domain (NC 1) through which two molecules are joined by disulfide bridges and non-reducible cross-links of an unknown nature resistant to intensive proteolytic attack, which would destroy interstitial collagen structures [15]. For example, treatment of mature collagen 1V with bacterial collagenase at 20°C leaves a long form of the 7s domain intact [15]. The a1 and ct2 chain components of this domain have been isolated and characterized [16].Here we present the complete amino acid sequence of the a1 chain of the long-form 7 s domain. From the primary structure of the 7s domain the mechanisms for the self assembly of collagen I...

Extensive structural differences between genes for the α1 and α2 chains of type IV collagen despite conservation of coding sequences

“…The amino acid sequence of the NC-1 domains of both chains from man [3][4][5] and mouse [6][7][8] sources has been reported. About 70°7o of the amino acid sequence for the collagenous part of the human [3,9,10] and about 30°7o of the mouse [5,11,12] eel(IV) chain have been reported and about 35°7o of the mouse oe2(IV) chain [13,14]. Sequence data have demonstrated that the NC-1 domains of the mammalian o'I(IV) and a,2(IV) chains share considerable interchain homology (63°7o) in the amino acid se-Volume 224, number 2…”

cDNA clones completing the nucleotide and derived amino acid sequence of the alpha 1 chain of basement membrane (type IV) collagen from mouse

“…The alpha 1 (IV) chain has no N-terminal globular domain, but starts with a telopeptide of 15 aa followed by the helical Gly-X-Y domain. The telopeptide contains 2 Lys and 4 Cys as reported [5] and is possibly the site of type IV collagen cross-linkage to form the basement membrane meshwork. The 7 S region has two interruptions in the Gly-X-Y repeat, ending at nt 732 with a large interruption of 13 aa, that sometimes is called NC2 domain [2].…”

“…The scaffold of the basement membrane is formed from type IV collagen molecules (review [2]) that cross-link head to head between the N-terminal (7 S) domains and tail to tail between the Cterminal (NCl) domains [3,4]. The aa sequence of the alpha 1 (IV) chain for the human 7 S region [5], but not for the N-terminus, and a partial aa sequence for the human [6] and the mouse [7] helical region has been published.…”

“…Thus the complete nt sequence of 5007 nt coding for the 1669 aa of the alpha 1 (IV) chain with a calculated M, of 160827 is known. The three differences with the partial mouse aa sequence [7] are shown in fig.2; the homology between the aa sequence of the human and the mouse is 93% for the 7 S region [5] and 88% for the triple helix [6].…”

“…Thus Lys (nt 82) at the beginning of the 7 S region [5] is created by the signal peptidase and not by the proteolytic enzymes used to isolate the 7 S protein. The alpha 1 (IV) chain has no N-terminal globular domain, but starts with a telopeptide of 15 aa followed by the helical Gly-X-Y domain.…”