Updated project metadata. Laminin, a ~800 kD heterotrimeric protein, is a major functional component of the extracellular matrix, contributing to tissue development and maintenance. We used cross-linking and mass spectrometry to determine the order of subunits in the ~750 Å trimeric coiled-coil oligomerization domain of laminin and to achieve an estimate of the register of the three subunits along the length of the coiled coil.