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Eric Xiaojia Wei, Zhenjun Zhao, Mark D. Willcox; The Effect of Metal Cations on Protein-Protein Interactions in Human and Rabbit Tears. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3731.
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Protein-protein interactions may play a role in tear film stability due to their effect on tear film viscosity. Metal cations in solution have an effect on protein-protein interactions and thus tear film stability. As rabbits have a more stable tear film than humans, we sought to examine the tears of rabbits and humans for protein-protein interactions, metal types and concentrations and how they affect protein-protein interactions.
Tears were collected from normal adult humans (n=10) and rabbits (n=6) using microcapillary tubes and pooled for each study group. Tear metal cations were analyzed using inductively coupled plasma (ICP) mass spectrometry and ICP atomic emission spectroscopy. Protein-protein interactions were studied using blue native-polyacrylamide gel electrophoresis (BN-PAGE). The effect of cations on protein-protein interactions was studied by using modified BN-PAGE in which cations were added to sample buffer and running buffer at levels of 0, human tears or rabbit tears.
Major metals in tears did not differ between species, however, rabbit tears had a higher concentration of divalent cations: [Mg2+], Human=0.39mM, Rabbit=1.13mM; [Ca2+], Human=0.38mM, Rabbit=0.75mM. In the absence of cations, protein-protein interactions were identified in both human (DMBT1-lactoferrin-lysozyme and lactoferrin-lipocalin) and rabbit tears (interactions of lipophilin subclasses). Additional protein-protein interactions were found in rabbit tears (prolactin inducible protein-lipophilins), but not in human tears, in the presence of cations at either of concentrations tested.
The presence of cations shows no effect on protein-protein interactions in human tears, but increases the protein-protein interactions in rabbit tears. However, the cation’s contribution to tear film stability needs further investigation.
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