Characterization of MRNP34, a novel methionine-rich nacre protein from the pearl oysters

Abstract

Nacre of the Pinctada pearl oyster shells is composed of 98% CaCO3 and 2% organic matrix. The relationship between the organic matrix and the mechanism of nacre formation currently constitutes the main focus regarding the biomineralization process. In this study, we isolated a new nacre matrix protein in P. margaritifera and P. maxima, we called Pmarg- and Pmax-MRNP34 (methionine-rich nacre protein). MRNP34 is a secreted hydrophobic protein, which is remarkably rich in methionine, and which is specifically localised in mineralizing the epithelium cells of the mantle and in the nacre matrix. The structure of this protein is drastically different from those of the other nacre proteins already described. This unusual methionine-rich protein is a new member in the growing list of low complexity domain containing proteins that are associated with biocalcifications. These observations offer new insights to the molecular mechanisms of biomineralization.

Novel Molluskan Biomineralization Proteins Retrieved from Proteomics: A Case Study with Upsalin

“…A similar situation has been observed previously with some members of the shematrin family and with the methionine-rich protein MRNP-34, [25] which are thought to provide frameworks for calcification. Shematrins-1, -2, -5, and -6 showed expression levels that were not restricted to the mantle but were also present in other tissues such as the adductor muscles.…”

“…[15,24] In addition to the identification of homologous proteins, proteomics on shell extracts has revealed a set of novel unknown proteins for which structure-function relations are far from elucidation. Examples include MUSPs-2 and -3 (edible mussel), [19] MRNP34 (pearl oyster), [25] and IMSPs-1, -2, and -3 (manila clam). [18] The growing number of these "orphan shell proteins", without known functions, highlights the need for their complete characterization, in order to understand their roles in biomineralization.…”

Evidence of donor effect on cultured pearl quality from a duplicated grafting experiment onPinctada margaritiferausing wild donors

“…Such differences in aragonite thickness and/or shell deposit rate have been observed for P. maragaritifera grown at different trophic levels (Linard et al 2011). This ability is driven by the mineralizing properties of the calcifying tissue (mantle for the shell and pearl sac for the cultured pearl), which has been actively studied for P. margaritifera in recent years (Joubert et al 2010;Marie et al 2011;Montagnani et al 2011). Given these results and the importance of cultured nacre thickness (pearl size) for the value of a cultured pearl, further studies should be conducted, such as qPCR-based expression studies of candidate genes implicated in high biomineralisation capabilities.…”

A History of the Cultured Pearl Industry

“…Parallel studies in the field of life science using genetic research have recently made rapid progress. In pearl research, genome analysis is also making rapid progress (Shen and Morse, 1997;Kono et al, 2000;Zhang and Zhang, 2003;Wang et al, 2008Wang et al, , 2009, and there have been many significant studies in the field of biomineralization, such as the elucidation of the nacre-forming mechanism (Suzuki et al, 2009;Jackson et al, 2010;Joubert et al, 2010;Kinoshita et al, 2011;Fang et al, 2011;Gardner et al, 2011;Montagnani et al, 2011;Isowa et al, 2012;Marie et al, 2012;Wang et al, 2012). An important milepost was reached in 2012 when, in a world first, a group including the Okinawa Institute of Science and Technology Graduate University and others performed draft genome sequencing of the Japanese Akoya oyster (Takeuchi et al, 2012).…”