Aspergillus nidulans
Protein Kinase C

Protein Kinase C (PKC) is a serine/threonine protein kinase, which phosphorylates cellular targets upon receipt of various upstream signals.  Targeting of PKC to specific sites in a cell is an important component of the regulation of PKC activity, both by bringing PKC into contact with potential activating factors and by influencing the range of substrates that are phosphorylated.

We have demonstrated that the genetic defect in the Aspergillus nidulans calC2 mutation is a point mutation in the A. nidulans orthologue of PKC, designated PkcA.  The mutation affects the C1B domain, causing hypersensitivity to Calcofluor White along with other drug sensitivities that indicate a defect in cell wall integrity (Teepe et al., 20007).  This suggests strong parallels to the Cell Wall Integrity signalling pathway of yeasts, in which PKC functions as a central player.

One of several examples of the calC2 mutant's elevated sensitivity to wall compromising agents is the excessive swelling of spores during germination in the presence of Caspofungin (inhibitor of glucan synthesis) and Tunicamycin (inhibitor of glycosylation).

A PkcA::GFP chimera localizes to hyphal apices and growing septa, as well as to the conidiogenous apices of phialides, indicating a role for PkcA in polarized cell wall growth.  These observations support the hypothesis that the role of PkcA in A. nidulans, is comparable to that played by Pkc1p in the Saccharomyces cerevisiae cell wall integrity pathway.

In each image pair, the color image shows localization of PkcA::GFP and the grayscale image the localization of chitin (stained with CFW).  The first pair illustrates PkcA targeting to hyphal apices - the remaining two pairs show dynamic localization to forming septa.

Current work under the direction of Loretta Jackson-Hayes has identified two specific regions of PkcA that are involved in targeting the protein to tips and/or septa (Jackson-Hayes et al., 2015).   Truncated versions of PkcA were produced carrying either N-terminal or C-terminal GFP tags, and monitored for ability to localize to tips or septa (see below).

Depicted are localization patterns of four different PKC truncations, demonstrating that some localize only to septa, some to both tips and septa (wild type localization), and some fail to localize to either site.

Analysis of the localization pattern identifies two specific regions that must be present in the PKC molecule in order to localize to one site or another.

A 10 amino acid sequence near the carboxyl end of the C2 domain, is required for localization to hyphal tips.  A second region between C2 and C1B (encompassing C1A) is sufficient for localization to septation sites, but not hyphal tips.

Literature:

Teepe, A. G., D. M. Loprete, Z.-M. He, T. A. Hoggard, and T. W. Hill.  2007.  "The protein kinase C orthologue PkcA plays a role in cell wall integrity and polarized growth in Aspergillus nidulans".   Fungal Genetics & Biology 44: 554-562.

Jackson-Hayes, L., T. W. Hill, D. M. Loprete, C. DelBove, J. Shapiro, J. Henley, and O. Dawodu.   2015.  "Two amino acid sequences direct Aspergillus nidulans protein kinase C (PkcA) localization to hyphal apices and septation sites."  Mycologia 107: 452-459.

Return to Lab Home Page

Link to Hill Homepage

Link to Jackson-Hayes Homepage