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Dissertation zugänglich unter
Structural variations in catalytic and ubiquitin –associated domains of Human protein kinase MARK1 and MARK3
Strukturelle Unterschiede in der katalytischen und Ubiquitin-assoziierten Domäne der humanen Proteinkinasen MARK1 und MARK3
Dokument 1.pdf (17.000 KB)
Freie Schlagwörter (Englisch):
Structure , MARK , UBA , Kinase , Human
Mandelkow, Eckhard (Prof. Dr.)
Tag der mündlichen Prüfung:
Kurzfassung auf Englisch:
MAP/Microtubule Affinity Regulating Kinases (MARK) are Ser/Thr kinases, which were discovered by their ability to phosphorylate tau and other MAPs in their KXGS motifs. Phosphorylation of tau, especially at Ser262, leads to strong reduction in the ability of tau to bind microtubules. Unbound tau aggregates into neurofibrillary tangles (NFTs), a hallmark of Alzheimer disease.
MARKs are involved in diverse cellular processes such as polarity, metabolism, cell cycle regulation and fertility. Disruption of MARK activities leads to deleterious effects in different kinds of cells. In humans, MARK is encoded by four isoforms and several splice variants. MARK kinases are relatively long proteins and exhibit a unique domain arrangement consisting of an N-terminal header, a kinase domain of Ser/Thr kinase architecture, an ubiquitin associated domain, and a tail or KA1 domain. The structure of MARK2 construct which comprised the catalytic and the UBA domain had shown that the kinase had a typical kinase bi-lobe structure consisting of an N- and a C-lobe and that the UBA domain binds at the distal side on the N-lobe. The binding of the UBA domain to the kinase enforces the kinase to be in catalytically nonproductive (open) conformation. The UBA domain was made of three alpha helices and an atypical fold in which the last helix was inverted as compared to the conventional UBA structures.
Two new isoforms of MARK were crystallized which also comprised the kinase and the UBA domain. MARK1 was crystallized using the wild type construct, whereas MARK3 was crystallized using a double alanine mutant. The alanine mutations were made on activation loop Thr and Ser residues (Thr208 and S212 residues of MARK2). Thr208 is the primary phosphorylation site of upstream kinases like MARKK and LKB1, and Ser212 is shown to be phosphorylated by GSK3-β. These isoforms crystallized in two different space groups, MARK1 in space group P212121 and MARK3 in space group C2.
The structure of MARK1 and MARK3 showed that, despite the completely different space group and packing of the molecules in these crystals, the overall conformation, folding and arrangement of the molecules is similar to MARK2. An analysis of the interaction elements in the crystals shows that, some of the structural elements like the activation loop, helix C and helix G by which the two molecules of MARK2 dimerize are conserved in the new MARK crystal structures.
These crystal structures also show that the UBA domain docks to the N-lobe of the kinase through hydrophobic contacts, with an atypical fold of the UBA domain in which the last helix is inverted, similar to MARK2. These kinases also crystallized in a catalytically nonproductive (open) conformation, but a different inactive state than MARK2 as indicated by the swing of helix C.
Small angle X-ray scattering analysis showed that the UBA domain binds to the N-lobe of the kinase even in solution, free of crystal constraints and that there are no major conformational rearrangement of the UBA domain in response to kinase activation. Kinase assays showed that, MARK1 and 2 kinases are activated to a greater extent on deleting the UBA domain than on retaining it. All these results are consistent with the crystal structures of MARK, with regard to the binding of the UBA domain and its role in enforcing an open, inactive conformation of the MARK kinases.