How do spores wake up? Proteins involved in the first stages of spore germination
|PhD ceremony:||Ms J.C. (Jeanette) Velasquez Guzman|
|When:||February 20, 2015|
|Supervisors:||prof. dr. B. (Bert) Poolman, prof. T. Abee|
|Where:||Academy building RUG|
|Faculty:||Science and Engineering|
The thesis of Jeanette Velásquez Guzmán aims to answer the question: how do spores wake up during germination? Her results provide for the first time clear biophysical and biochemical evidence for channel-like activity of SpoVA proteins. She proposes that SpoVAC facilitates the release of Ca-DPA and other low molecular weight compounds during germination.
Germinant receptors are involved in nutrient uptake in the early steps of the germination process. Velásquez has used several biochemical approaches to uncover the function of the germinant receptor proteins of the GerA family from Bacillus subtilis. Unfortunately, the instability of GerA proteins after purification precluded a full assessment of their function(s). The stability and folding of GerAC was tested by means of microcalorimetry and spectroscopy methods. On the basis of in silico homology modeling, the relative instability of GerAC can be rationalized from its structure. The function of the protein for which the crystal structure is available is still elusive.
Another key step in spore germination is the release of calcium-dipicolinic acid (Ca-DPA), presumably by SpoVA proteins. This process takes place within the first minutes of spore germination. Velásquez cloned and expressed the genes of several SpoVA membrane proteins and obtained sub-milligram amounts of protein for biochemical analysis. She presents strong evidence that SpoVAC has channel activity and may be responsible for Ca-DPA release during germination. SpoVAC provides protection against hypoosmotic stress and functions as a mechanosensitive channel protein. Furthermore, SpoVAC responds to the asymmetric insertion into the membrane of the amphiphiles lysoPC and dodecylamine.