Trujillo Laboratory Leibniz Institute of Plant Biochemistry Independent Research Group Ubiquitin is a small (7.5 kDa) and highly conserved protein modifier. Attachment of ubiquitin by the  ubiquitination system (UBS) which is composed by a three step enzymatic cascade condemns tagged  proteins to degradation or to other fates, such as endocytosis or relocalization in the cell.  Ubiquitination (aka. ubiquitylation) is a posttranslational modification that determines a novel fate of the  modified target protein. Conjugation of Ubiquitin, which is a small (7.5 kDa) and highly conserved protein  modifier, is the common denominator of all three major proteolysis pathways in eukaryotes, as well as   mediate changes in activity or intracellular localization. Ubiquitination rivals phosphorylation in scope and  glycosylation in complexity.   Ubiquitination is involved in all aspects of cellular life and its staggering complexity is paralleled by the  significance of its functions in molecular processes.  Ubiquitination of a target protein (T) involves a sequential cascade of enzymatic activities. The ubiquitin-  activating enzyme (E1) forms a thioester linkage with the ubiquitin (red). Next, ubiquitin is passed to a  ubiquitin-conjugating enzyme (E2) again through a thioester linkage. The E2 carries the activated ubiquitin  to the ubiquitin ligase (E3), which facilitates the transfer of the ubiquitin from the E2 to a lysine residue  in the target protein. The E3 is generally considered to control the target specificity, while the E2 dictates  which type of ubiquitination takes place. In most cases, proteins marked with a K48 linked ubiquitin chain  are destined for degradation through the 26S proteasome. Polyubiquitination through K63 residues of  ubiquitin and multi-monomeric ubiquitination lead to regulatory events.   The UBS plays a key role in the regulation of processes triggered during plant immune responses and the  integration of signaling for example through changes in hormone levels. The main goal of our group is the  functional analysis of UBS components involved in the modulation of immune responses and the  identification of proteins targeted for ubiquitination.  Plants are in constant interaction with microbes, some of which are capable to infect them and cause  disease. The invasion by microbes is perceived through receptors that recognize so called pathogen  associated molecular patterns (PAMPs), such as flagellin, lipopolysacharides and chitin. Activation of these  receptors triggers a plethora of reactions, which culminate in the activation of the so called PAMP-  triggered immunity (PTI). Pathogenic microorganisms have developed means to counter PTI by delivering  virulence effector proteins or compounds that suppress immune responses into the plant cell. In an “arms  race” plants evolved another subset of receptors that detect effectors or their activities and activate an  effector-triggered immunity (ETI). Ubiquitination has been reported to play manifold functions as depicted  below. Ubiquitination of molecular components involved in the signal transduction and the deployment of both  PTI and ETI, plays a central regulatory role. Our research focuses on E3 ubiquitin ligases (E3s). The  attachment of ubiquitin, called ubiquitination, is mediated by an enzymatic cascade in which the E3s  mediate the addition of ubiquitin and at the same time define the target protein.  Our group has defined a set of related plant u-box type E3 ligases (PUBs) that act as negative regulators of  PAMP triggered signaling and PTI. Several responses are de-repressed in plants mutated in pub22-24 genes.  These responses include the oxidative burst, MAP kinase 3 (MPK3) activity and transcriptional activation of  marker genes. The de-repression of responses is common to the perception of several PAMPs indicating  that it regulates a process common to different receptors.  We are currently engaged in various approaches to elucidate the manifold functions of the UMS, including  the identification and analysis of novel PUBs targets with functions in the immune response. Furthermore,  we are elucidating the basis of ubiquitination process itself and how it is regulated.  Info Lab Tour twitter Links Internal