REVIEW Biomineralization proteins: from vertebrates to bacteria Lijun WANG (✉), Marit NILSEN-HAMILTON Ames Laboratory, U. S. Department of Energy, Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA 50011, USA © Higher Education Press and Springer-Verlag Berlin Heidelberg 2012 Abstract Biomineralization processes are frequently found in nature. Living organisms use various strategies to create highly ordered and hierarchical mineral structures under physiologic conditions in which the temperatures and pressures are much lower than those required to form the same mineralized structures by chemical synthesis. Although the mechanism of biomineralization remains elusive, proteins have been found responsible for the formation of such mineral structures in many cases. These proteins are active components in the process of biomineralization. The mechanisms by which their function can vary from providing active organic matrices that control the formation of specific mineral structures to being catalysts that facilitate the crystallization of certain metal ions. This review summarizes the current understanding of the functions of several representative biomineralization proteins from vertebrates to bacteria in the hopes of providing useful insight and guidance for further elucidation of mechanisms of biomineralization processes in living organisms. Keywords biomineralization proteins, structure-function relationships, self-assembly, nanoparticles Introduction The term biomineralization refers to the processes by which living organisms produce mineral structures that usually exist as pure inorganic materials in nature (Weiner, 2008). The size, morphology, composition and location of the minerals produced by living organisms are controlled by genetic factors and determined by biologic entities that are usually proteinaceous (Miller and Parker, 1984; Addadi and Weiner, 1985; Simmer and Fincham, 1995; Cha et al., 1999; Mahamid et al., 2010). Most biomineralization processes take place under physiologic conditions where the temperatures and pressures are much lower than those required to form the same mineralized structures in the absence of organic materials. The high degree of control by biologic systems over the crystallization of inorganic elements is of interest from both the biologic and material science perspective. Although the mechanisms of biomineralization remain elusive, results of recent investigations have begun to shed light on these fascinating processes (Gower, 2008; Weiner, 2008; Bonucci, 2009). Minerals formed by living organisms from bacteria to vertebrates can be classified into three major categories: calcium, silicon and iron (Gower, 2008). The morphologies and structures of these biominerals are as diverse as the living organisms that produce them. In those cases for which there is some understanding of the biologic mechanisms involved in biomineralization, proteins have been found responsible for forming the mineral structures (Addadi and Weiner, 1985; Weiner and Addadi, 1991; Gorski, 1992; Weaver and Morse, 2003; Moradian-Oldak et al., 2006; Weiner, 2006; Weiner, 2008). The mechanisms by which mineralization proteins function are poorly understood, but they have been proposed to include the control of size, morphology, orientation, composition and the localization of crystals synthesized by organisms (Weiner, 2008; Cölfen, 2010). The role of proteins in the biomineralization process is critical considering that biomineralization occurs readily under mild physiologic conditions compared with the high temperatures and pressures required to produce the same products in vitro (Gower, 2008). The focus of this review is to provide a brief summary of the current understanding of the functions of proteins in some selected mineralization processes of biologic systems. We will discuss the roles of collagen and amelogenin in the Received January 4, 2012; accepted May 2, 2012 Correspondence: Lijun WANG E-mail: wlj@iastate.edu Front. Biol. DOI 10.1007/s11515-012-1205-3