English: Capping proteins (CP) play a major role in regulating actin filament dynamics by blocking the addition and loss of actin subunits. Two major variants of CP have been determined: a cytoplasmic form that is also termed Cap32/34 and an isoform found in the Z-discs of skeletal muscle that is often called CapZ. CP is a heterodimeric protein that is expressed in all eukaryotic organisms. The crystal structure of CapZ has provided valuable insight into the atomic architecture of CP found at the Z-discs of skeletal muscles. However, until now a high-resolution structure of the cytoplasmic variant has not been available. By characterizing the atomic structure of Cap32/34 from the cellular slime mold Dictyostelium discoideum as a model for cytoplasmic CP and comparing it to that of CapZ, structural and functional differences between the two CP isoforms can be elucidated. This image shows orthogonal views of Cap32/34 superposed onto CapZ over the Cα positions of the entire CP molecules.

From "Conservation and divergence between cytoplasmic and muscle-specific actin capping proteins: insights from the crystal structure of cytoplasmic Cap32/34 from Dictyostelium discoideum"

Christian Eckert, Agnieszka Goretzki, Maria Faberova and Martin Kollmar

BMC Structural Biology 2012, 12:12

http://www.biomedcentral.com/1472-6807/12/12/abstract