Plants grown at high densities perceive a decrease in the red to far-red (R:FR) ratio of incoming light, resulting from absorption of red light by canopy leaves and reflection of far-red light from neighboring plants. These changes in light quality trigger a series of responses known collectively as the shade avoidance syndrome. During shade avoidance, stems elongate at the expense of leaf and storage organ expansion, branching is inhibited, and flowering is accelerated. We identified several loci in Arabidopsis, mutations in which lead to plants defective in multiple shade avoidance responses. Here we describe TAA1, an aminotransferase, and show that TAA1 catalyzes the formation of indole-3-pyruvic acid (IPA) from L-tryptophan (L-Trp), the first step in a previously proposed, but uncharacterized, auxin biosynthetic pathway. This pathway is rapidly deployed to synthesize auxin at the high levels required to initiate the multiple changes in body plan associated with shade avoidance.
Pin1 contains an N-terminal WW domain and a C-terminal peptidyl-prolyl cis-trans isomerase (PPIase) domain connected by a flexible linker. To address the energetic and structural basis for WW domain recognition of phosphoserine (P.Ser)/phosphothreonine (P. Thr)- proline containing proteins, we report the energetic and structural analysis of a Pin1-phosphopeptide complex. The X-ray crystal structure of Pin1 bound to a doubly phosphorylated peptide (Tyr-P.Ser-Pro-Thr-P.Ser-Pro-Ser) representing a heptad repeat of the RNA polymerase II large subunit's C-terminal domain (CTD), reveals the residues involved in the recognition of a single P.Ser side chain, the rings of two prolines, and the backbone of the CTD peptide. The side chains of neighboring Arg and Ser residues along with a backbone amide contribute to recognition of P.Ser. The lack of widespread conservation of the Arg and Ser residues responsible for P.Ser recognition in the WW domain family suggests that only a subset of WW domains can bind P.Ser-Pro in a similar fashion to that of Pin1.
Protein folding barriers result from a combination of factors including unavoidable energetic frustration from nonnative interactions, natural variation and selection of the amino acid sequence for function, and͞or selection pressure against aggregation. The rate-limiting step for human Pin1 WW domain folding is the formation of the loop 1 substructure. The native conformation of this six-residue loop positions side chains that are important for mediating protein-protein interactions through the binding of Pro-rich sequences. Replacement of the wild-type loop 1 primary structure by shorter sequences with a high propensity to fold into a type-I -turn conformation or the statistically preferred type-I G1 bulge conformation accelerates WW domain folding by almost an order of magnitude and increases thermodynamic stability. However, loop engineering to optimize folding energetics has a significant downside: it effectively eliminates WW domain function according to ligand-binding studies. The energetic contribution of loop 1 to ligand binding appears to have evolved at the expense of fast folding and additional protein stability. Thus, the two-state barrier exhibited by the wild-type human Pin1 WW domain principally results from functional requirements, rather than from physical constraints inherent to even the most efficient loop formation process.-turn ͉ ligand binding ͉ protein folding ͉ -sheet ͉ protein function G lobular proteins evolve by mutation and selection. Selection criteria include function, and sufficient thermodynamic stability and folding rate to avoid sustained chaperone binding and proteasome degradation. The selection criteria cannot always be optimized independently over the entire sequence of a protein. For the human Pin1 (hPin1) WW domain (Pin WW hereafter), we have shown that residues important for stability and folding rate are segregated in the sequence (1-4). It is likely that functional selection criteria are predominant once minimal energetic criteria are met. Therefore, sequence evolution to enhance function may lead to a decrease in protein stability and folding rate compared with a sequence optimized for folding energetics.The hPin1 cell cycle regulatory proline (Pro) cis͞trans-isomerase is a two-domain protein (5). In its physiological role, the N-terminal WW domain binds Pro-rich ligands of the consensus sequence (pS͞pT)P, whereas the C-terminal domain catalyzes the Pro cis͞ trans-isomerization at the pS͞pT-P peptide bond. NMR solution studies show that the two domains, which are connected by a flexible solvated linker, interact only weakly before ligand binding (6, 7). The structure of the isolated Pin WW domain is virtually superimposable on that of the WW domain in the two-domain hPin1 protein (8). Moreover, Pin WW exhibits sufficient thermodynamic stability for biophysical analysis, folds rapidly, and retains its ligand-binding function (3, 9). These attributes, combined with sequence information on Ͼ150 WW domain family members (10, 11), makes Pin WW an excellent small model p...
Structural and functional characterization of 2-PS together with generation of a CHS mutant with an initiation/elongation cavity analogous to 2-PS demonstrates that cavity volume influences the choice of starter molecule and controls the final length of the polyketide. These results provide a structural basis for control of polyketide length in other PKSs, and suggest strategies for further increasing the scope of polyketide biosynthetic diversity.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.