Amino acid racemization reveals differential protein turnover in osteoarthritic articular and meniscal cartilages

Stäbler, Thomas; Byers, Samuel S; Zura, Robert; Kraus, Virginia B.

doi:10.1186/ar2639

Cited by 27 publications

(30 citation statements)

References 22 publications

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“…Asx and Ser, in particular, showed substantial age-dependent racemisation. This is the first report of D-Ser in lenses, although it increases with age in articular cartilage and dentin (Stabler et al 2009). On average, the total number of racemised Asx, Ser and Thr residues in crystallins from a 70-year-old normal lens, amounted to two or three D-amino acids per polypeptide chain.…”

Section: Discussionmentioning

confidence: 67%

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Racemisation and human cataract. d-Ser, d-Asp/Asn and d-Thr are higher in the lifelong proteins of cataract lenses than in age-matched normal lenses

Hooi

Truscott

2010

AGE

107

122

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Astract Several amino acids were found to undergo progressive age-dependent racemisation in the lifelong proteins of normal human lenses. The two most highly racemised were Ser and Asx. By age 70, 4.5% of all Ser residues had been racemised, along with >9% of Asx residues. Such a high level of inversion, equivalent to between 2 and 3 D -amino acids per polypeptide chain, is likely to induce significant denaturation of the crystallins in aged lenses. Thr, Glx and Phe underwent age-dependent racemisation to a smaller degree. In model experiments, D -amino acid content could be increased simply by exposing intact lenses to elevated temperature. In cataract lenses, the extent of racemisation of Ser, Asx and Thr residues was significantly greater than for agematched normal lenses. This was true, even for cataract lenses removed from patients at the earliest ages where age-related cataract is observed clinically. Racemisation of amino acids in crystallins may arise due to prolonged exposure of these proteins to ocular temperatures and increased levels of racemisation may play a significant role in the opacification of human lenses.

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Section: Discussionmentioning

confidence: 67%

“…7 and 8), as well as Val and Ile (data not shown), displayed no significant age-dependent racemisation. In cartilage, levels of D-Leu were reported to increase slightly with age (Stabler et al 2009). Asn/Asp displayed the greatest level of racemisation.…”

Section: Discussionmentioning

confidence: 99%

Racemisation and human cataract. d-Ser, d-Asp/Asn and d-Thr are higher in the lifelong proteins of cataract lenses than in age-matched normal lenses

Hooi

Truscott

2010

AGE

107

122

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“…An age-dependent increase in D-Ser residues was also demonstrated for proteins in articular cartilage and tooth dentin [29,30].…”

Section: Introductionmentioning

confidence: 97%

Racemization of Serine Residues Catalyzed by Dihydrogen Phosphate Ion: A Computational Study

Takahashi¹,

Kirikoshi²,

Manabe³

2017

Catalysts

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Spontaneous, nonenzymatic reactions in proteins are known to have relevance to aging and age-related diseases, such as cataract and Alzheimer's disease. Among such reactions is the racemization of Ser residues, but its mechanism in vivo remains to be clarified. The most likely intermediate is an enol. Although being nonenzymatic, the enolization would need to be catalyzed to occur at a biologically relevant rate. In the present study, we computationally found plausible reaction pathways for the enolization of a Ser residue where a dihydrogen phosphate ion, H 2 PO 4 − , acts as a catalyst. The H 2 PO 4 − ion mediates the proton transfer required for the enolization by acting simultaneously as both a general base and a general acid. Using the B3LYP density functional theory method, reaction pathways were located in the gas phase and hydration effects were evaluated by single-point calculations using the SM8 continuum model. The activation barriers calculated for the reaction pathways found were around 100 kJ mol −1 , which is consistent with spontaneous reactions occurring at physiological temperature. Our results are also consistent with experimental observations that Ser residue racemization occurs more readily in flexible regions in proteins.

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“…Racemized Asx (aspartate and asparagine) concentrations in cartilage extracts were quantified using a previously described HPLC approach developed and validated in our laboratory [24]. Briefly, the insoluble and soluble cartilage proteins were acid hydrolyzed in 6M HCl at 105 C for 6 h. The resulting free D-and L-amino acids were derivatized to fluorescent compounds by addition of o-phthaldialdehyde and N-tert-butyloxycarbonyl-Lcysteine.…”

Section: Quantification Of Racemized Amino Acidsmentioning

confidence: 99%

“…Racemization refers to the timedependent conversion of amino acids in proteins from the L form to the D form (only L amino acids are incorporated into mammalian proteins). Cartilage, a tissue with low turnover due to its aneural and avascular nature, undergoes quantifiable racemization of some amino acids during the lifespan [24,25]. Recent advances in the field of biomarkers of ageing and turnover have demonstrated that COMP is a useful determinant of differential turnover between hip and knee, with knee cartilage showing a greater turnover response than hip cartilage [21].…”

Section: Introductionmentioning

confidence: 99%

Cartilage biomarkers in the osteoarthropathy of alkaptonuria reveal low turnover and accelerated ageing

et al. 2016

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Objective. Alkaptonuria (AKU) is a rare autosomal recessive disease resulting from a single enzyme deficiency in tyrosine metabolism. As a result, homogentisic acid cannot be metabolized, causing systemic increases. Over time, homogentisic acid polymerizes and deposits in collagenous tissues, leading to ochronosis. Typically, this occurs in joint cartilages, leading to an early onset, rapidly progressing osteoarthropathy. The aim of this study was to examine tissue turnover in cartilage affected by ochronosis and its role in disease initiation and progression.Methods. With informed patient consent, hip and knee cartilages were obtained at surgery for arthropathy due to AKU (n = 6; 2 knees/4 hips) and OA (n = 12; 5 knees/7 hips); healthy non-arthritic (non-OA n = 6; 1 knee/5 hips) cartilages were obtained as waste from trauma surgery. We measured cartilage concentrations (normalized to dry weight) of racemized aspartate, GAG, COMP and deamidated COMP (D-COMP). Unpaired AKU, OA and non-OA samples were compared by non-parametric MannWhitney U test.Results. Despite more extractable total protein being obtained from AKU cartilage than from OA or non-OA cartilage, there was significantly less extractable GAG, COMP and D-COMP in AKU samples compared with OA and non-OA comparators. Racemized Asx (aspartate and asparagine) was significantly enriched in AKU cartilage compared with in OA cartilage.Conclusions. These novel data represent the first examination of cartilage matrix components in a sample of patients with AKU, representing almost 10% of the known UK alkaptonuric population. Compared with OA and non-OA, AKU cartilage demonstrates a very low turnover state and has low levels of extractable matrix proteins.

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Amino acid racemization reveals differential protein turnover in osteoarthritic articular and meniscal cartilages

Cited by 27 publications

References 22 publications

Racemisation and human cataract. d-Ser, d-Asp/Asn and d-Thr are higher in the lifelong proteins of cataract lenses than in age-matched normal lenses

Racemisation and human cataract. d-Ser, d-Asp/Asn and d-Thr are higher in the lifelong proteins of cataract lenses than in age-matched normal lenses

Racemization of Serine Residues Catalyzed by Dihydrogen Phosphate Ion: A Computational Study

Cartilage biomarkers in the osteoarthropathy of alkaptonuria reveal low turnover and accelerated ageing

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