Proline

H-Pro-OH

Proline: a multifunctional amino acid.[Pubmed:20036181]

Trends Plant Sci. 2010 Feb;15(2):89-97.

Proline accumulates in many plant species in response to environmental stress. Although much is now known about Proline metabolism, some aspects of its biological functions are still unclear. Here, we discuss the compartmentalization of Proline biosynthesis, accumulation and degradation in the cytosol, chloroplast and mitochondria. We also describe the role of Proline in cellular homeostasis, including redox balance and energy status. Proline can act as a signaling molecule to modulate mitochondrial functions, influence cell proliferation or cell death and trigger specific gene expression, which can be essential for plant recovery from stress. Although the regulation and function of Proline accumulation are not yet completely understood, the engineering of Proline metabolism could lead to new opportunities to improve plant tolerance of environmental stresses.

HIFalpha targeted for VHL-mediated destruction by proline hydroxylation: implications for O2 sensing.[Pubmed:11292862]

Science. 2001 Apr 20;292(5516):464-8.

HIF (hypoxia-inducible factor) is a transcription factor that plays a pivotal role in cellular adaptation to changes in oxygen availability. In the presence of oxygen, HIF is targeted for destruction by an E3 ubiquitin ligase containing the von Hippel-Lindau tumor suppressor protein (pVHL). We found that human pVHL binds to a short HIF-derived peptide when a conserved Proline residue at the core of this peptide is hydroxylated. Because Proline hydroxylation requires molecular oxygen and Fe(2+), this protein modification may play a key role in mammalian oxygen sensing.

Elicitor- and wound-induced oxidative cross-linking of a proline-rich plant cell wall protein: a novel, rapid defense response.[Pubmed:1623521]

Cell. 1992 Jul 10;70(1):21-30.

Treatment of bean or soybean cells with fungal elicitor or glutathione causes a rapid insolubilization of preexisting (hydroxy)Proline-rich structural proteins in the cell wall. This insolubilization, which involves H2O2-mediated oxidative cross-linking, is initiated within 2 min and is complete within 10 min under optimal conditions, and hence, precedes the expression of transcription-dependent defenses. Cross-linking is also under developmental control during hypocotyl growth and in tissues subject to mechanical stress such as the stem-petiole junction. Stimulus-dependent oxidative cross-linking of wall structural proteins is a novel site of cellular regulation with potentially important functions in cell maturation and toughening of cell walls in the initial stages of plant defense.

Proline isomerization of histone H3 regulates lysine methylation and gene expression.[Pubmed:16959570]

Cell. 2006 Sep 8;126(5):905-16.

The cis-trans isomerization of Proline serves as a regulatory switch in signaling pathways. We identify the Proline isomerase Fpr4, a member of the FK506 binding protein family in Saccharomyces cerevisiae, as an enzyme which binds the amino-terminal tail of histones H3 and H4 and catalyses the isomerization of H3 Proline P30 and P38 in vitro. We show that P38 is necessary for methylation of K36 and that isomerization by Fpr4 inhibits the ability of Set2 to methylate H3 K36 in vitro. These results suggest that the conformational state of P38, controlled by Fpr4, is important for methylation of H3K36 by Set2. Consistent with such an antagonistic role, abrogation of Fpr4 catalytic activity in vivo results in increased levels of H3K36 methylation and delayed transcriptional induction kinetics of specific genes in yeast. These results identify Proline isomerization as a novel noncovalent histone modification that regulates transcription and provides evidence for crosstalk between histone lysine methylation and Proline isomerization.