Document Type

Honors Thesis


Coral bleaching is an immune response where compromised algal symbionts are expelled from host tissue. Porites astreoides and Orbicella faveolata are model species on opposing ends of the immunity spectrum. Disease-resistant P. astreoides employs adaptive autophagic mechanisms when immunocompromised, while disease-sensitive O. faveolata activates caspase-mediated apoptosis. Presented here is a characterization of caspase homologs found in disease-tolerant P. astreoides (P.ast-3, P.ast-7) and disease-susceptible P. astreoides (O.fav-3a, O.fav-3b). P.ast-7 and O.fav-3a are unusual in that they retain high sequence similarity to human executioner caspases but possess a CARD-like domain characteristic of initiator and inflammatory caspases. Results indicate that P.ast-7 and O.fav-3a are monomers preferring aspartate in the P1 substrate position, corroborated by low activity against canonical caspase substrate Ac-DEVD-AFC. O.fav-3b and P.ast-3 are dimers preferring valine in P1, but inactivity against Ac-VEID-AFC suggests additional specificity. A crystal structure of P.ast-7 bound with DEVD-CHO reveals two potential regulatory sites: first, a unique insertion of RYP residues was found to form hydrogen bonds with the substrate, and second, an N-terminal peptide bound near the active site is hypothesized to serve as an exosite. This study of basal metazoan caspases is pertinent to understanding the phenomenon of coral bleaching, as well as the evolution of human caspase substrate specificity and regulatory mechanisms.

Publication Date






To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.