Is protein methylation in the human lens a result of non-enzymatic methylation by S-adenosylmethionine?
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Is protein methylation in the human lens a result of non-enzymatic methylation by S-adenosylmethionine? / Truscott, Roger J W; Mizdrak, Jasminka; Friedrich, Michael G; Hooi, Michelle Y; Lyons, Brian; Jamie, Joanne F; Davies, Michael Jonathan; Wilmarth, Phillip A; David, Larry L.
In: Experimental Eye Research, Vol. 99, 06.2012, p. 48-54.Research output: Contribution to journal › Journal article › Research › peer-review
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TY - JOUR
T1 - Is protein methylation in the human lens a result of non-enzymatic methylation by S-adenosylmethionine?
AU - Truscott, Roger J W
AU - Mizdrak, Jasminka
AU - Friedrich, Michael G
AU - Hooi, Michelle Y
AU - Lyons, Brian
AU - Jamie, Joanne F
AU - Davies, Michael Jonathan
AU - Wilmarth, Phillip A
AU - David, Larry L
N1 - Copyright © 2012 Elsevier Ltd. All rights reserved.
PY - 2012/6
Y1 - 2012/6
N2 - Since crystallins in the human lens do not turnover, they are susceptible to modification by reactive molecules over time. Methylation is a major post-translational lens modification, however the source of the methyl group is not known and the extent of modification across all crystallins has yet to be determined. Sites of methylation in human lens proteins were determined using HPLC/mass spectrometry following digestion with trypsin. The overall extent of protein methylation increased with age, and there was little difference in the extent of modification between soluble and insoluble crystallins. Several different cysteine and histidine residues in crystallins from adult lenses were found to be methylated with one cysteine (Cys 110 in γD crystallin) at a level approaching 70%, however, methylation of crystallins was not detected in fetal or newborn lenses. S-adenosylmethionine (SAM) was quantified at significant (10-50 μM) levels in lenses, and in model experiments SAM reacted readily with N-α-tBoc-cysteine and N-α-tBoc-histidine, as well as βA3-crystallin. The pattern of lens protein methylation seen in the human lens was consistent with non-enzymatic alkylation. The in vitro data shows that SAM can act directly to methylate lens proteins and SAM was present in significant concentrations in human lens. Thus, non-enzymatic methylation of crystallins by SAM offers a possible explanation for this major human lens modification.
AB - Since crystallins in the human lens do not turnover, they are susceptible to modification by reactive molecules over time. Methylation is a major post-translational lens modification, however the source of the methyl group is not known and the extent of modification across all crystallins has yet to be determined. Sites of methylation in human lens proteins were determined using HPLC/mass spectrometry following digestion with trypsin. The overall extent of protein methylation increased with age, and there was little difference in the extent of modification between soluble and insoluble crystallins. Several different cysteine and histidine residues in crystallins from adult lenses were found to be methylated with one cysteine (Cys 110 in γD crystallin) at a level approaching 70%, however, methylation of crystallins was not detected in fetal or newborn lenses. S-adenosylmethionine (SAM) was quantified at significant (10-50 μM) levels in lenses, and in model experiments SAM reacted readily with N-α-tBoc-cysteine and N-α-tBoc-histidine, as well as βA3-crystallin. The pattern of lens protein methylation seen in the human lens was consistent with non-enzymatic alkylation. The in vitro data shows that SAM can act directly to methylate lens proteins and SAM was present in significant concentrations in human lens. Thus, non-enzymatic methylation of crystallins by SAM offers a possible explanation for this major human lens modification.
KW - Adolescent
KW - Adult
KW - Aged
KW - Aging
KW - Chromatography, High Pressure Liquid
KW - Cysteine
KW - Histidine
KW - Humans
KW - Lens, Crystalline
KW - Mass Spectrometry
KW - Methylation
KW - Middle Aged
KW - Protein Methyltransferases
KW - Protein Processing, Post-Translational
KW - Proteomics
KW - S-Adenosylmethionine
KW - Tissue Donors
KW - Young Adult
KW - beta-Crystallin A Chain
U2 - 10.1016/j.exer.2012.04.002
DO - 10.1016/j.exer.2012.04.002
M3 - Journal article
C2 - 22542751
VL - 99
SP - 48
EP - 54
JO - Experimental Eye Research
JF - Experimental Eye Research
SN - 0014-4835
ER -
ID: 128974982