Graduate student Ana Castro defends thesis

Ana Castro with Professor Craig Ellermeier

Ana Castro successfully defended her PhD thesis, "The role of the anti-sigma factor RsiV in stress response in Clostridium difficile and Bacillus subtilis," on Monday, March 26, 2018. Ana is pictured here with her mentor, Dr. Craig Ellermeier.


Extra cytoplasmic function (ECF) σ factors are a diverse family of alternative σ factors that allow bacteria to sense and respond to changes in the environment. σV is an ECF σ factor found primarily in low GC Gram-positive bacteria, induces resistance to lysozyme and is important for virulence in several pathogens. In the absence of lysozyme, σV is inhibited by the anti-σ factor RsiV. In response to lysozyme, RsiV is degraded by regulated intramembrane proteolysis (RIP). RIP is initiated by signal peptidase cleavage of RsiV at site-1 which allows the Site-2 protease RasP to cleave RsiV within the membrane and leads to activation of σV. We seek to understand the molecular mechanisms that allow signal peptidase to cleave RsiV only in the presence of lysozyme. We demonstrate in vitro that signal peptidase is sufficient for cleavage of RsiV only in the presence of lysozyme. We determined that the cleavage of RsiV by signal peptidase increases with lysozyme concentration. We also demonstrate that multiple signal peptidases are sufficient for cleavage of RsiV in the presence of lysozyme.

The lab previously determined the X-ray crystal structure of the extracellular domain of RsiV in complex with lysozyme. This revealed that RsiV does not bind near the signal peptidase cleavage site. This led to a putative model in which binding of lysozyme by RsiV triggers a conformational change which allows signal peptidase to recognize a previously hidden cleavage site. We are investigating this possibility by determining the structure of full-length RsiV and full-length sV-RsiV in the absence and presence of lysozyme. Together these approaches will provide information on the changes that occur to RsiV upon binding lysozyme that lead to σV activation. This study will broaden our knowledge on a novel role for signal peptidase and could lead to novel drug targets.


About Ana

Ana was born in Miami, Florida and moved to San Pedro Sula, Honduras where she spent most of her childhood. She is the youngest of four children and spent most of her time fighting with her brothers. At a young age, Ana enjoyed spending a lot of time reading, playing with friends, and getting her siblings in trouble (she was really good at this!). She attended Thomas Jefferson High School in Cedar Rapids, IA where her interest in science began.

Ana attended Clarke University in Dubuque, IA to pursue a degree in Biology and Biochemistry. In the summer of 2010, Ana worked as an REU student in Dr. Rosemary Stuart’s lab at Marquette University. Here, she studied the localization  of yeast ADP/ATP carrier proteins tagged with GFP in S. cerevisiae. In 2012, Ana enrolled in the Department of Biology graduate program at the University of Nebraska at Omaha where she obtained a Masters of Science degree in Biology. She worked with Dr. Bruce Chase and investigated the localization of the mind-meld gene during the early developmental stages of Drosophila melanogaster embryos.

In 2014 Ana began her Master’s work at Iowa eventually found a home in Dr. Craig Ellermeier’s lab, studying extra cytoplasmic function (ECF) σ factors in Bacillus subtiils. Being such an avid and loyal Iowa fan, Ana was unaware that Dr. Ellermeier was an Iowa State fan prior to joining the lab. Regardless, she has had fun decorating his office every time Iowa beat Iowa State in football (she has pictures). During her time in the Ellermeier lab, she has worked on developing an in vitro cleavage assay to detect the cleavage of the anti-sigma factor RsiV by signal peptidase. 

Outside of the lab, Ana enjoys spending time with her fiancée, Cory,  and her many nieces and nephews. She enjoys watching soccer, football, baseball, and hockey. Ana and Cory enjoy hiking, going to sporting events, traveling, trying new restaurants and constantly debating about how superior the Chicago Cubs are compared to the St. Louis Cardinals (Cory is unfortunately a St. Louis Cardinals fan). Ana and Cory are looking forward to getting married in the Fall 2018.



Tuesday, April 3, 2018