Abstract by Anders Drabæk Wiuf
Transport of transition metals across cellular membranes plays a fundamental role in maintaining homeostasis of both toxic and essential metals including zinc, a pivotal micronutrient for all living organisms. ZIP proteins constitute an indispensable family of zinc-transporting membrane proteins, which assists in controlling numerous physiological and cellular functions. Moreover, malfunction of human ZIPs is linked to severe genetic disorders and cancer. However, due to the poor expression and stability of ZIPs, the mechanistic basis for ZIP-mediated zinc flux remains poorly understood. The overarching aim of this thesis is to improve our structural and functional understanding of ZIP transporters.
Towards this goal, I report a procedure to establish overproduction of prokaryotic and eukaryotic ZIPs in yeast. I show that Saccharomyces cerevisiae is a superior host for overproduction of prokaryotic membrane proteins and capable of rescuing expression of ZIP transporters.
The major finding of this thesis is the proposal of the general transport mechanism of ZIP transporters, which has been a subject of debate. I suggest that ZIP transporters are elevator transporters, consisting of a transport and a scaffold/domain. With the first determined inwardopen metal free structure of a ZIP transporter, I find zinc dependant vertical rigid-body- like
movements of the transport domain, relative to the dimer/scaffold domain. Furthermore, I show, with a combination of molecular dynamics simulations and evolutionary coupling analysis, that our crystal structure reflects the biological dimer, and that the oligomerization interface is the scaffold/dimer domain. Surprisingly, the structure also revealed a novel 9th N-terminal
transmembrane segment, which may be important for expression and function of the transporter.
The work in thesis successfully shed new light on the structure and function of ZIP transporters at the molecular level. Furthermore, the established overproduction procedures and in-vivo-based functional assays provide a framework for follow-up more in-depth basic science investigations of the structure and function of ZIPs, and for downstream translational efforts, perhaps allowing rational drug-design for treatment of ZIP-related disorders.