Protein transport and folding: Proteins are formed as long chains of amino acids that fold into very specific three-dimensional conformations, which are essential for their activity. In the crowded cellular environment, proteins are assisted by chaperone proteins to fold into their final, functional conformation [1, 2]. Nascent proteins take advantage of chaperone proteins to reach their functional structure, as do stress-denatured proteins. Additionally, most proteins that are transported across biological membranes traverse the membrane in an unfolded conformation [3-8]. The processes of unfolding for transport and refolding on the other side of the membrane both make use of chaperone proteins. Our laboratory focuses on two types of protein systems: the 60 kDa protein-folding system and the mitochondrial inner-membrane protein import system.
Protein folding by Cpn60: The 60 kDa family of chaperone proteins, also known as "chaperonins", is composed of two types. We are studying type I chaperonins, tetradecameric oligomeric proteins composed of 60 kDa subunits (cpn60) that work together with small heptameric ring-shaped helper proteins composed of 10 kDa (cpn10) subunits [9, 10]. This system is over-expressed in response to heat-shock, prevents protein aggregation and helps stress-denatured proteins refold. Thus, the proteins are also called the 60 and 10 kDa heat-shock proteins (hsp's). Due to their tremendous stability, the best studied of these proteins are the GroEL (60 kDa subunits) and GroES (10 kDa subunits) of E. coli. Homologous proteins have been identified in mammalian, yeast and plant mitochondria as well as in plant chloroplasts [11, 12]. In our laboratory, we are studying the structure and function of mammalian mitochondrial and plant chloroplast chaperonins, both of which exhibit different structural characteristics than GroEL.
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