Prefoldin Recognition Motifs in the Nonhomologous Proteins of the Actin and Tubulin Families

Abstract

Nascent actin and tubulin molecules undergo a series of complex interactions with chaperones and are thereby guided to their native conformation. These cytoskeletal proteins have the initial part of the pathway in common: both interact with prefoldin and with the cytosolic chaperonin containing tailless complex polypeptide 1. Little is understood with regard to how these chaperones and, in particular, prefoldin recognize the non-native forms of these target proteins. Using mutagenesis, we provide evidence that ␤-actin and ␣-tubulin each have two prefoldin interaction sites. The most amino-terminally located site of both proteins shows striking sequence similarity, although these proteins are nonhomologous. Very similar motifs are present in ␤-and ␥-tubulin and in the newly identified prefoldin target protein actin-related protein 1. Actin-related proteins 2 and 3 have related motifs, but these have altered charge properties. The latter two proteins do not bind prefoldin, although we identify them here as target proteins for the cytosolic chaperonin. Actin fragments containing the two prefoldin interaction regions compete efficiently with actin for prefoldin binding. In addition, they also compete with tubulins, suggesting that these target proteins contact similar prefoldin subunits.

Prefoldin 6 is required for normal microtubule dynamics and organization in Arabidopsis

“…Other eukaryotic PFD complexes bind to nascent chains and assist folding of actin and tubulin (4,5,7). In our 2D-DIGE analysis using pfd6-1, actins were not identified among the down-regulated proteins and actin organization was not obviously changed in pfd6-1 as compared with wild type (data not shown).…”

Microarray analysis of the developing cortex

“…These peak levels are maintained as the animal matures and reaches adulthood, implying that protein folding and intracellular signaling functions are required at a stable level throughout life. Prefoldin 2 (Pfdn2) is a hetero-hexameric chaperone that assists with proper folding of proteins by trafficking them to cytosolic chaperonins (Vainberg et al, 1998;Hansen et al, 1999;Rommelaere et al, 2001;Martin-Benito et al, 2002). Another coexpressed gene is the prefoldin 5 (Pfdn5) subunit, which binds to the transcription factor c-Myc, and consequently represses its E-box dependent transcriptional activity (Mori et al, 1998;Fujioka et al, 2001).…”

PhLP3 Modulates CCT-mediated Actin and Tubulin Folding via Ternary Complexes with Substrates

“…The actin-related proteins represent candidates responsible for such indirect effects. Actin-related proteins regulate actin filament nucleation and organization, and some actin-related proteins are known CCT and prefoldin substrates (49). Alternatively, the speed and timing of actin production may be dysregulated in the absence of PFD and Plp1p, leading to defects in filament organization and function.…”