Abstract
Dictyostelium discoideum is gaining increasing attention as a model organism for the study of calcium binding and calmodulin function in basic biological events as well as human diseases. After a short overview of calcium-binding proteins, the structure of Dictyostelium calmodulin and the conformational changes effected by calcium ion binding to its four EF hands are compared to its human counterpart, emphasizing the highly conserved nature of this central regulatory protein. The calcium-dependent and -independent motifs involved in calmodulin binding to target proteins are discussed with examples of the diversity of calmodulin binding proteins that have been studied in this amoebozoan. The methods used to identify and characterize calmodulin binding proteins is covered followed by the ways Dictyostelium is currently being used as a system to study several neurodegenerative diseases and how it could serve as a model for studying calmodulinopathies such as those associated with specific types of heart arrythmia. Because of its rapid developmental cycles, its genetic tractability, and a richly endowed stock center, Dictyostelium is in a position to become a leader in the field of calmodulin research.
Highlights
Calcium mediates aspects of almost all cellular functions in eukaryotes
To understand cellular evolution and the success of multicellular organisms, it is essential to understand the evolution of calcium signaling [1,2,3,4]
Data mining reveals that all protists, including Dictyostelium, possess proteins that have the same types of calcium binding domains found in both plants and animals [3]
Summary
Calcium mediates aspects of almost all cellular functions in eukaryotes. To understand cellular evolution and the success of multicellular organisms, it is essential to understand the evolution of calcium signaling [1,2,3,4]. Data mining reveals that all protists, including Dictyostelium, possess proteins that have the same types of calcium binding domains found in both plants and animals [3]. A group of penta-EF CaBPs have five, rather than four, contiguous helix-loop-helix calcium-binding motifs; due to amino acid variants, some of the EF hands may be unable to bind the divalent cation. A smaller group of proteins have been shown to possess non-canonical calcium binding sites in various species, but none have been yet characterized in Dictyostelium. While 14 CaBPs (Cbp1-14) have been identified these are but a small part of the approximately five dozen calcium-binding proteins that have been detected in this organism (Unitprot.org; dictyBase.org). MlcD (147aa, 16.5 kDa) is similar in size and shares 44% sequence identity but it does not bind calcium. MlcB (73aa, 8.3 kDa) is like a single lobe of CalA, while MlcB (147aa, 16.5 kDa) has two lobes but only one binds calcium
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