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Damian J Krysan

Publications and source records attributed to Damian J Krysan.

6 recordsLinked to original sources
PubMed2005

Yapsins are a family of aspartyl proteases required for cell wall integrity in Saccharomyces cerevisiae.

The yeast cell wall is a crucial extracellular organelle that protects the cell from lysis during environmental stress and morphogenesis. Here, we demonstrate that the yapsin family of five glycosylphosphatidylinositol-linked aspartyl proteases is required for cell wall integrity in Saccharomyces cerevisiae. Yapsin null mutants show hypersensitivity to cell wall perturbation, and both the yps1Delta2Delta mutant and the quintuple yapsin mutant (5ypsDelta) undergo osmoremedial cell lysis at 37 degrees C. The cell walls of both 5ypsDelta and yps1Delta2Delta mutants have decreased amounts of 1,3- and 1,6-beta-glucan. Although there is decreased incorporation of both 1,3- and 1,6-beta-glucan in the 5ypsDelta mutant in vivo, in vitro specific activity of both 1,3- and 1,6-beta-glucan synthesis is similar to wild type, indicating that the yapsins affect processes downstream of glucan synthesis and that the yapsins may be involved in the incorporation or retention of cell wall glucan. Presumably as a response to the significant alterations in cell wall composition, the cell wall integrity mitogen-activated kinase signaling cascade (PKC1-MPK pathway) is basally active in 5ypsDelta. YPS1 expression is induced during cell wall stress and remodeling in a PKC1-MPK1-dependent manner, indicating that Yps1p is a direct, and important, output of the cell wall integrity response. The Candida albicans (SAP9) and Candida glabrata (CgYPS1) homologues of YPS1 complement the phenotypes of the yps1Delta mutant. Taken together, these data indicate that the yapsins play an important role in glucan homeostasis in S. cerevisiae and that yapsin homologues may play a similar role in the pathogenic yeasts C. albicans and C. glabrata.

Aspartic Acid Endopeptidases↗
PubMed2004

Plasticity of extended subsites facilitates divergent substrate recognition by Kex2 and furin.

Yeast Kex2 and human furin are subtilisin-related proprotein convertases that function in the late secretory pathway and exhibit similar though distinguishable patterns of substrate recognition. Although both enzymes prefer Arg at P(1) and basic residues at P(2), the two differ in recognition of P(4) and P(6) residues. To probe P(4) and P(6) recognition by Kex2p, furin-like substitutions were made in the putative S(4) and S(6) subsites of Kex2. T252D and Q283E mutations were introduced to increase the preference for Arg at P(4) and P(6), respectively. Glu(255) was replaced with Ile to limit recognition of P(4) Arg. The effects of putative S(4) and S(6) mutations were determined by examining the cleavage by purified mutant enzymes of a series of fluorogenic substrates with systematic changes in P(4) and/or P(6). Whereas wild Kex2 exhibited little preference type for Arg at P(6), the T252D mutant and T252D/Q283E double mutant exhibited clear interactions with P(6) Arg. Moreover, the T252D and T252D/Q283E substitutions altered the influence of the P(6) residue on P(4) recognition. We infer that cross-talk between S(4) and S(6), not seen in furin, allows wild type and mutant forms of Kex2 to adapt their subsites for altered modes of recognition. This apparent plasticity may allow the subsites to rearrange their local environment to interact with different substrates in a productive manner. E255I-Kex2 exhibited significantly decreased recognition of P(4) Arg in a tetrapeptide substrate with Lys at P(1), although the general pattern of selectivity for aliphatic residues at P(4) remained unchanged.

Amino Acid Sequence↗
PubMed2002

Claims of equivalence in randomized controlled trials of the treatment of bacterial meningitis in children.

OBJECTIVE: To evaluate claims of therapeutic equivalence in studies of the treatment of bacterial meningitis in children. METHODS: We performed a systematic review of randomized controlled trials of antimicrobial therapy for bacterial meningitis in children indexed in MEDLINE and published after 1980 and that claimed equivalency. The sample size of each trial was compared with the minimum sample size needed to rigorously claim equivalence. The primary endpoint was case fatality. RESULTS: Twenty-five studies were identified that met the inclusion criteria. Two of these were specifically designed to test equivalence, and the remaining based claims of equivalence on failed tests of superiority. The majority of these trials (24 of 25) that claimed equivalence had sufficient sample size to exclude a 20% difference in mortality between the tested therapies. Only 3 of the 25 trials could exclude a 10% difference in mortality. CONCLUSION: Few of the trials in this study had sufficient sample size to claim equivalence within 10% of the expected mortality. Proving equivalency is challenging because large sample sizes are often needed to ensure adequate statistical power to rule out clinically important differences between the standard of care and new therapies.

Anti-Bacterial Agents↗