Atomic force microscopy of collagen molecules. Surface morphology of segment-long-spacing (SLS) crystallites of collagen.

Three-dimensional structures of laterally aggregated bundles of collagen molecules, segment-long-spacing (SLS) crystallites, were imaged by atomic force microscopy (AFM) in atmosphere. The overall image of the type I collagen SLS in a height-amplified mode was semi-cylindrical, approximately 300 nm in length, with two bands of elevation near both N- and C- ends of the molecule. Its 'cross-sectional' profile (across the molecular axis) was a smooth arch. The 'axial' profile (along the molecular axis) had two prominent peaks approximately 250 nm apart, corresponding to the two bands of elevation. There were several minor peaks between these two prominent peaks. The elevation near both ends may be due to the presence of covalently bound sugars near both N- and C- ends of the helical part of type I collagen alpha chains. The AFM images of SLS presented here indicate that the type I collagen molecule is not uniform in diameter and has two bulged parts within its triple helix.