Laminins are the major noncollagenous components of basement membranesthat mediate cell adhesion growth migration and differentiation. They arecomposed of distinct but related alpha beta and gamma chains. The threechains form a cross-shaped molecule that consist of a long arm and three shortglobular arms. The long arm consist of a coiled coil structure contributed byall three chains and cross-linked by interchain disulphide bonds.Beside different types of globular domains each subunit contains in its firsthalf consecutive repeats of about 60 amino acids in length that include eightconserved cysteines . The tertiary structure of this domain isremotely similar in its N-terminal to that of the EGF-like module (see ). It is known as a 'LE' or 'laminin-type EGF-like' domain. Thenumber of copies of the LE domain in the different forms of laminins is highlyvariable; from 3 up to 22 copies have been found.A schematic representation of the topology of the four disulphide bonds inthe LE domain is shown below.
+-------------------+ +-|-----------+ | +--------+ +-----------------+ | | | | | | | | xxCxCxxxxxxxxxxxCxxxxxxxCxxCxxxxxGxxCxxCxxgaagxxxxxxxxxxxCxx sssssssssssssssssssssssssssssssssss'C': conserved cysteine involved in a disulphide bond'a': conserved aromatic residue'G': conserved glycine (lower case = less conserved)'s': region similar to the EGF-like domain
In mouse laminin gamma-1 chain the seventh LE domain has been shown to be theonly one that binds with a high affinity to nidogen
. The binding-sites arelocated on the surface within the loops C1-C3 and C5-C6
. Longconsecutive arrays of LE domains in laminins form rod-like elements of limitedflexibility
which determine the spacing in the formation of lamininnetworks of basement membranes