5 research outputs found
Amelogenin Processing by MMP-20 Prevents Protein Occlusion Inside Calcite Crystals
Calcite crystals were grown in the presence of full-length
amelogenin
and during its proteolysis by recombinant human matrix metalloproteinase
20 (rhMMP-20). Recombinant porcine amelogenin (rP172) altered the
shape of calcite crystals by inhibiting the growth of steps on the
{104} faces and became occluded inside the crystals. Upon co-addition
of rhMMP-20, the majority of the protein was digested resulting in
a truncated amelogenin lacking the C-terminal segment. In rP172-rhMMP-20
samples, the occlusion of amelogenin into the calcite crystals was
drastically decreased. Truncated amelogenin (rP147) and the 25-residue
C-terminal domain produced crystals with regular shape and less occluded
organic material. Removal of the C-terminal diminished the affinity
of amelogenin to the crystals and therefore prevented occlusion. We
hypothesize that hydroxyapatite (HAP) and calcite interact with amelogenin
in a similar manner. In the case of each material, full-length amelogenin
binds most strongly, truncated amelogenin binds weakly, and the C-terminus
alone has the weakest interaction. Regarding enamel crystal growth,
the prevention of occlusion into maturing enamel crystals might be
a major benefit resulting from the selective cleavage of amelogenin
at the C-terminus by MMP-20. Our data have important implications
for understanding the hypomineralized enamel phenotype in cases of <i>amelogenesis imperfecta</i> resulting from MMP-20 mutations
and will contribute to the design of enamel inspired biomaterials
Tooth enamel protein amelogenin binds to ameloblast cell membrane-mimicking vesicles via its N-terminus
α-Synuclein Populates Both Elongated and Broken Helix States on Small Unilamellar Vesicles
The misfolding of the protein α-synuclein (αS) has been implicated in the molecular chain of events leading to Parkinson disease. Physiologically, αS undergoes a transition from a random coil to helical conformation upon encountering synaptic vesicle membranes. On analogous small unilamellar vesicles (SUVs), the conformation of αS is dominated by a single elongated αS helix. However, alternative broken helix states have been postulated, mandating experimental clarification. Here, the upper limit for the free energy difference between elongated and broken helix conformations on SUVs resembling synaptic vesicles was determined to be 1.2 ± 0.4 kcal/mol, which amounts to a population ratio of 7.6:1 between both states (12% broken helices). In response to helix breaks at different positions, αS rearranged in an opportunistic manner, thereby minimizing helix abrogations to as little as one to two turns. Enthalpy and entropy measurements of gel state SUV-αS interactions indicated that broken helix states retain the ability to relieve membrane-packing stress. Thus, broken helix states are a distinct physiological feature of the vesicle-bound αS state, making it a “checkered” protein of multiple parallel conformations. A continuous interconversion between structural states may contribute to pathological αS misfolding
Amelogenin processing by MMP-20 prevents protein occlusion inside calcite crystals
10.1021/cg300754aCrystal Growth and Design12104897-4905CGDE