Flavohemoglobin Expression and Function in Saccharomyces cerevisiae

Abstract

The yeast Saccharomyces cerevisiae contains a flavohemoglobin, encoded by the gene YHB1, whose function is unclear. Previous reports presented evidence that its maximal expression requires disruption of mitochondrial respiration and that it plays a role in the response to oxidative stress. We have studied the expression of YHB1 in respiratory deficient cells and in cells exposed to various compounds causing oxidative stress. Several different strains and approaches (spectroscopic detection of the oxygenated form of Yhb1p, ␤-galactosidase activity of a YHB1-lacZ fusion, and Northern blot analysis) were used to demonstrate that YHB1 expression and Yhb1p production are not increased by respiration deficiency. YHB1 expression was unchanged in cells challenged with antimycin A or menadione, while it decreased in cells exposed to H 2 O 2 , diamide, dithiothreitol, and Cu 2؉ . Transcription of YHB1 is not under the control of the transcriptional factor Yap1p. These results do not support a participation of YHB1 in the genetic response to oxidative stress. We also analyzed the growth phenotypes associated with altered Yhb1p production using YHB1-deleted strains and strains that greatly overproduced Yhb1p. Yhb1p appears to protect cells against the damage caused by Cu 2؉ and dithiothreitol, while sensitizing them to H 2 O 2 . Yhb1p overproduction in a glucose-6-phosphate dehydrogenase-deficient mutant decreased its growth rate. These data indicate that there is a complex relationship(s) between Yhb1p function(s) and cell defense reactions against various stresses.

Vitreoscilla Hemoglobin Binds to Subunit I of Cytochrome bo Ubiquinol Oxidases

“…In any case, it now appears that the roles and functions of VHb are more complex than just the oxygen-transporting one initially believed. These hypothetical functions are different from the NO detoxification function proposed for flavohemoproteins from E. coli (22)(23)(24)(25)(26)(27). A recent study, however, indicates that NO detoxification may be a secondary but important function for VHb (28), whereas its primary function may be oxygen transfer, as supported by the data presented here.…”

Characterization of a New Hemoprotein in the YeastSaccharomyces cerevisiae

“…In contrast, transcription of the Saccharomyces cerevisiae flavohemoglobin, encoded by the YHB1 gene, is enhanced under oxygen-replete conditions via the hemedependent activation of the HAP1 and HAP2/3/4 transcription factors (10). Recently, it has been proposed that this flavohemoglobin might play a role in the oxidative stress response in yeast (11), but discrepancies in the results between different laboratories do not allow this conclusion (12); however, the results of phenotypic studies on YHB1-deleted or overexpressing strains suggest a complex relationship between Yhb1p function and cell defense against various stresses (12).…”

Protection from nitrosative stress by yeast flavohemoglobin

“…YHB1 is not required for respiration, fermentation, or growth under any O 2 tension (20)(21)(22). It has been suggested that YHB1 may protect against oxidative stress (20), but this function has been questioned (21,22). Herein, we report that yeast YHB1 is required to metabolize NO and thereby protects against nitrosylation of cellular targets and inhibition of cell growth under both aerobic and anaerobic conditions.…”

“…The expression of the yeast flavohemoglobin gene YHB1 is elevated under aerobic conditions (20,21), whereas E. coli hmp expression is not affected by O 2 (12). YHB1 is not required for respiration, fermentation, or growth under any O 2 tension (20)(21)(22). It has been suggested that YHB1 may protect against oxidative stress (20), but this function has been questioned (21,22).…”