Book of Abstracts: Albany 2011
June 14-18 2011
©Adenine Press (2010)
Structural Studies of Nucleic Acid-Binding Proteins Involved in Regulating Cell Differentiation and Pluripotency
Transcription factors play a central role in regulating cell differentiation and de-differentiation. The use of "cocktails" of transcription factors to promote the reprogramming of adult fibroblasts into induced pluripotent stem cells (iPS) has generated tremendous interest in biology and medicine. The originally reported sets of iPS generating factors contained Oct4, Sox2, Klf4 and c-Myc (1) or Oct4, Sox2, Nanog and Lin28 (2). Here we report on structural and biochemical studies of two of these proteins, Klf4 and Lin28.
Klf4 (Krueppel-like factor 4) is a zinc-finger transcription factor required for the maturation of epithelial tissues. Crystal structure analyses of two different zinc-finger fragments of Klf4 reveal that the two C-terminal C2H2 zinc-finger motifs of Klf4 are required for DNA site specificity and the induction of macrophage differentiation (3). The N-terminal zinc finger, conversely, inhibits the otherwise cryptic self-renewal capacity of Klf4. A Klf4 zinc-finger domain mutant induces self-renewal and block of cell maturation.
Lin28 is a highly conserved RNA-binding protein and was described to modulate the processing of let-7 microRNA precursors (4). The small protein contains a cold-shock domain (CSD) and a tandem array of retroviral-type CCHC zinc fingers. Both protein motifs are presumably involved in RNA binding. Crystal structure analysis reveals that the Lin28 CSD resembles the bacterial cold shock proteins (5-8). The presence of conserved nucleotide-binding subsites of the surface of Lin28 CSD suggests a common mode of DNA or RNA single-strand binding of Lin28 and bacterial cold shock proteins (9, 10).
Macromolecular Structure and Interaction Group
Max-Delbrück Center for Molecular Medicine
Robert-Rössle-Str. 10, 13125 Berlin, Germany