Functional and Molecular Insights of Hydrogen Sulfide Signaling and Protein Sulfhydration

Abstract

Hydrogen sulfide (H2S), a novel gasotransmitter, is endogenously synthesized by multiple enzymes that are differentially expressed in the peripheral tissues and central nervous systems. H2S regulates a wide range of physiological processes, namely cardiovascular, neuronal, immune, respiratory, gastrointestinal, liver, and endocrine systems, by influencing cellular signaling pathways and sulfhydration of target proteins. This review focuses on the recent progress made in H2S signaling that affects mechanistic and functional aspects of several biological processes such as autophagy, inflammation, proliferation and differentiation of stem cell, cell survival/death, and cellular metabolism under both physiological and pathological conditions. Moreover, we highlighted the cross-talk between nitric oxide and H2S in several bilogical contexts.

Keywords: CBS; CSE; hydrogen sulfide; sulfhydration.

Figure 1

Intracellular syntheis of H2S by CBS, CSE and MST. L-cysteine serves as a substrate for all three enzymes to produce H2S in cells; however, homocysteine can be used as a substrate to synthesize H2S by the enzymatic activity of CSE and CBS.

Figure 2

The principle of red maleimide assay to detect sulfhydration of proteins. In this method, red malimide interacts with both –SH and -SSH groups and forms –S-Mal and –S-S-Mal respectively. Upon treatment with DTT, the –S-Mal will remain unaltered, however, –S-S-Mal will be cleaved off to form –SH and –S-Mal as the products. Thus the sulfhydrated protein will lose the signal of red fluorescence of red maleimide. A cartoon image (right side) of a gel showing that the red intensity of a target protein remains unaltered in the presence or absence of DTT in samples untreated with H2S. On the other hand, the red fluorescent intensity of protein will be lost after DTT treatment in samples treated with H2S. The residual red fluorescent intensity before and after DTT tretament divided by total protein will provide the percentage of sulfhydration of protein.

Figure 3

Sulfhydration of proteins in general. Box 1: Sulfhydration of Keap1 leads Nrf2 to translocate to the nucleus and synthesize antioxidant genes. Box 2: sulfhydration of a E3 ligase, Parkin protein leads to degradation of its substrates and provides neuroprotection. Box 3: sulfhydration of p65 (NFkB) stimulates its transcriptional activation after its interaction with RPS3 protein. Box 4: sulfhydration of GAPDH leads to degradation of PSD95 after its interaction with a E3 ligase Siah protein. This event leads to memmory imapirment following an induction of a proinflammatory cytokine, IL-1β. Box 5: sulfhydration of a channel protein TRPV6 regulates maintenace of stem cell function via modulating β-catenin inside cells. Box 6: Sulfhydration of PTP1B induces PERK phopshorylation and triggers ER stress which has been implicated in several neurodegenerative diseases. Box 7: Sulfhydration of IRF1 serves as a transcriptional suppressor and facilititates the transcriptional activation of TFAM which is impaortant for mitochondrial DNA compaction.

Figure 4

Two contrasting examples how nitrosylation and sulfhydration of proteins affect the biological processes. (A) sulfhydration of GAPDH leads to degradation of PSD95 via Siah. In contrast nitrosylation of GAPDH leads to cell death via activating p300/CBP and p53 signaling axis. (B) sulfhydration of p65 interacts with RPS3 and facilitates transcriptional activation of p65. On the other hand, nitrosylation of p65 prevents its transcriptional activation.