Transgelin (TAGLN), also known as smooth muscle protein 22 (SM22), is a highly conserved protein found in smooth muscle tissues of adult vertebrates. Abolition of transgelin gene expression by the oncogenic Ras may be an important early event in tumor progression and a diagnostic marker for breast and colon cancer development. Transgelin contains a single calponin homology (C H) domain. However, the question of whether this single CH domain can bind actin remains open. Here we report the 2.3 angstrom resolution crystal structure of full length human transgelin, whose main structural feature is confirmed to be a CH domain. Secondary structures of CH domains from different proteins were analyzed and conserved residues were identified that maintain similar tertiary structures. (c) 2008 Elsevier Inc. All rights reserved.