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Abstract
The complete amino acid sequence of the human laminin B2 chain has been determined by sequencing of cDNA clones. The six overlapping clones studied cover approximately 7.5 kilobases of which 5312 nucleotides were sequenced from the 5' end. The open reading frame codes for a 33-residue signal peptide and a 1576-residue B2 chain proper, which is 189 residues less than in the highly homologous B1 chain (Pikkarainen, T., Eddy, R., Fukushima, Y., Byers, M., Shows, T., Pihlajaniemi, T., Saraste, M., and Tryggvason, K. (1987) J. Biol. Chem. 262, 10454-10462). Computer analysis revealed that the B2 chain consists of distinct domains that contain helical structures, cysteine-rich repeats, and globular regions, as does the B1 chain. However, domain alpha and domain beta of the B1 chain have no counterpart in B2, and the number of cysteine-rich repeats is 12, or 1 less than in the B1 chain. The degree of homology between the two chains is highest in the cysteine repeat-containing domains III and V where 40% of the residues match. However, results demonstrate that the B1 and B2 chains of laminin are highly homologous proteins that are probably the products of related genes.
Highlights
COMPARISON OF THE COMPLETE AMINO ACID SEQUENCEWITH THE B1 CHAIN REVEALS VARIABILITY IN SEQUENCE HOMOLOGY BETWEENDIFFERENTSTRUCTURAL DOMAINS*
Laminin interacts with the other basement membrane components, type IV collagen, heparan sulfate proteoglycan, and entactin, with heparin and with other laminin molecules cysteine-rich repeats is 12, or 1 less than in the B1 [7,10,16,17,18]
Thefor heparan sulfate has been attributed to theglobule at the results demonstrate that theB1 and B2 chains of lam- end of the long arm [20,21].The central part of the cross and inin are highly homologous proteins that are probablythe distal part of the long arm have been shown to have the products of relategdenes
Summary
Terminal ends together form the long arm in a helical struc- Materials-Restriction endonucleases andT4 ligasewere purture, theA chain projecting into thelarge globule of the long chased from Boehringer Mannheim. The complete amino acid sequences for the mouse and human B1 chains have recently been reported [7,8] and the secondary structure based on these data are inaccordance with the electron microscopic findings. Isolation ofcDNA Clone.+” human placenta cDNA Iibrary cloned in Xgtll bacteriophage (Clonetech) was screened with a 0.7-kb’ cDNA clone (PEQ) thatcodes for part of the mouse laminin B2 chain [9]. Human Laminin B2 C h i n using the M13 cloning procedure [25] and the dideoxynucleotide chain termination method [26].
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