Laminins are a major constituent of all basement membranes. The polymerisation of
laminins at the cell surface is mediated by the three short arms of the cross-shaped
laminin heterotrimer. The short arms contain repeats of laminin-type epidermal
growth factor-like (LE) domains, interspersed with globular domains of unknown
function. A single LF domain is inserted between LE5 and LE6 of the laminin β1 and
β2 chains. We report the crystal structure at 1.85 Å resolution of the laminin β2
LE5-LF-LE6 region. The LF domain consists of a β-sandwich related to bacterial
family 35 carbohydrate binding modules, and more distantly to the L4 domains
present in the short arms of laminin α and γ chains. An α-helical region mediates the
extensive interaction of the LF domain with LE5. The relative arrangement of LE5
and LE6 is very similar to that of consecutive LE domains in uninterrupted LE
tandems. Fitting atomic models to a low-resolution structure of the first eight domains
of the laminin β1 chain determined by small-angle X-ray scattering suggests a
deviation from the regular LE array at the LE4-LE5 junction. These results advance
our understanding of laminin structure.