Tight binding of proteins to membranes from older human cells

Abstract

The lens is an ideal model system for the study of macromolecular aging and its consequences for cellular function, since there is no turnover of lens fibre cells. To examine biochemical processes that take place in the lens and that may also occur in other long-lived cells, membranes were isolated from defined regions of human lenses that are synthesised at different times during life, and assayed for the presence of tightly bound cytosolic proteins using quantitative iTRAQ proteomics technology. A majority of lens beta crystallins and all gamma crystallins became increasingly membrane bound with age, however, the chaperone proteins alpha A and alpha B crystallin, as well as the thermally-stable protein, βB2 crystallin, did not. Other proteins such as brain-associated signal protein 1 and paralemmin 1 became less tightly bound in the older regions of the lens. It is evident that protein-membrane interactions change significantly with age. Selected proteins that were formerly cytosolic become increasingly tightly bound to cell membranes with age and are not removed even by treatment with 7 M urea. It is likely that such processes reflect polypeptide denaturation over time and the untoward binding of proteins to membranes may alter membrane properties and contribute to impairment of communication between older cells.

Proteomics and Phosphoproteomics Analysis of Human Lens Fiber Cell Membranes

“…Even though the lens membrane fractions have been washed by 8 M urea and 0.1 M NaOH, significant amounts of crystallins are still associated with the membrane as reported by Truscott et al 19 In the current work, aA-Crystallin and bB1-crystallin have the largest spectral counts. aB-, bA3-, bA4-, bB2-, bS-, cCand cD-Crystallins also have high spectral counts (see Supplementary Material and Supplementary Tables S1a, S1b, http://www.iovs.org/lookup/suppl/doi:10.1167/iovs.…”

“…15,16 Membrane proteins are normally underrepresented in the majority of proteome profiles due to their extreme hydrophobicity. 17,18 In addition, crystallins and high abundance cytoskeletal proteins such as filensin and CP49 are strongly associated with the membrane protein fraction, 19 resulting in the dilution of membrane protein signals. Recently, a membrane proteomics approach was utilized to produce descriptions of membrane signatures in the mouse lens fiber cells and 232 proteins were found enriched or unique in the lens membrane fraction.…”

Structural and Functional Properties, Chaperone Activity and Posttranslational Modifications of Alpha-Crystallin and its Related Subunits in the Crystalline Lens: N-acetylcarnosine, Carnosine and Carcinine act as Alpha- Crystallin/Small Heat Shock Protein Enhancers in Prevention and Dissolution of Cataract in Ocular Drug Delivery Formulations of Novel Therapeutic Agents

“…The chaperone properties of alpha-crystallin are thought to allow the lens to tolerate aging-induced deterioration of the lens proteins without showing signs of cataracts until older age [9]. A majority of lens beta crystallins and all gamma crystallins are increasingly membrane bound with age, however, the chaperone proteins alpha A and alpha B crystallin, as well as the thermally-stable protein, B2 crystallin, are not associated with the membranes with age [228].…”

Small molecules, both dietary and endogenous, influence the onset of lens cataracts

“…The α-crystallins influence the head group organization of the phospholipids (Zhu et al, 2010a). Other lens proteins also become associated as the membranes age (Truscott et al, 2011) and it is thought that this will also contribute to the complexity of the protein complement on the membranes in aged lenses. Zhao et al (2015) found that applying lanosterol, but not cholesterol, to the eyes of dogs with age related (non-diabetic) cataract, cells transfected with mutant αA-crystallin and to ex vivo cataractous rabbit lens resulted in solubilization of the cataracts and solubilisation of the protein aggregates.…”