Since August 2013:
Prof. Dr. rer. nat.
Institute of Veterinary Physiology
Freie Universitšt Berlin
Oertzenweg 19b, Hs. 11
14163 Berlin, Germany
Grants German Research Foundation (DFG)
Other research topics
In previous work, the cloned mammalian H+/peptide transporters, PepT1 and PepT2, and the Ca2+-inactivated Cl- channel CaIC were analysed electrophysiologically employing the voltage clamp technique on oocytes of the African clawed toad Xenopus laevis:
Peptide transporters PepT1 and PepT2
@ Prof. Hannelore Daniel, Dept. Physiology of Nutrition, TU Munich, Weihenstephan
Primarily, PepT1 and PepT2 were characterized functionally. These experiments focused on transport of differently charged dipeptides in order to represent the vast number of possible substrates. Major differences of substrate affinities, pH- and potential dependence of transport were detected electrophysiologically.
Amasheh S, Wenzel U, Boll M, Dorn D, Weber WM, Clauss W, Daniel H (1997) Transport of charged dipeptides by the intestinal H+/peptide symporter PepT1 expressed in Xenopus laevis oocytes. J. Membr. Biol. 155: 247-256 [Medline Abstract]
Amasheh S, Weber WM, Wenzel U, Clauss W, Daniel H (1997) Electrophysiological analysis of a mammalian renal peptide transporter expressed in Xenopus laevis oocytes. J. Physiol. 504: 169-174 [Medline Abstract]
Based on the results of the comparative electrophysiological characterisation of PepT1 and PepT2, structure-function relationships were investigated using the chimeric approach. In this series of experiments, the first 90 amino acids of the N-terminal region have been shown to be responsible for substrate recognition. Furthermore, an uncoupling of transport characteristics was achieved.
Doering F, Dorn D, Bachfischer U, Amasheh S, Herget M, Daniel H (1996) Functional analysis of a chimeric mammalian peptide transporter derived from the intestinal and renal isoforms. J. Physiol. 497: 773-779 [Medline Abstract]
Doering F, Walter J, Foecking M, Amasheh S, Daniel H (1998) The aminoterminal region of the renal peptide transporter PepT2 determines its high substrate affinity. Nova Acta Leopoldina 78: 269-274
Both transporters displayed electrogenic transport of delta-aminolevulinic acid. This porphyrin precursor is used in the photodynamic therapy of tumors and does not contain a peptide bond. In further experiments, the minimal structural requirements of substrate molecules were investigated. Experiments perfusing a series of different fatty acid molecules showed that amino-fatty acids of a molecular length between 500 and 630 pm satisfy the structural requirements of peptide transporters.
Doering F, Will J, Amasheh S, Clauss W, Ahlbrecht H, Daniel H (1998) Minimal molecular determinants of substrates for recognition by the intestinal peptide transporter. J. Biol. Chem. 273: 23211-23218 [Medline Abstract]
Doering F, Walter J, Will J, Foecking M, Amasheh S, Clauss W, Daniel H (1998) Delta-aminolevulinic acid transport by intestinal and renal peptide transporters and its physiological and clinical implications. J. Clin. Invest. 101: 2761-2767 [Medline Abstract]
The Ca2+-inactivated Cl- channel CalC
@ Prof. Dr. Wolf-Michael Weber, present address: Institute of Animal Physiology, Electrophysiology and Molecular Biology Lab, University Muenster
Basic requirement for the use of Xenopus laevis oocytes as an expression system is the knowledge of transport systems already present in the oocyte membrane. The Ca2+-inactivated Cl- channel CaIC endogenous to the oocyte membrane possesses characteristics unique among Xenopus laevis channel proteins. The following publications in part focus on inhibitors potentially important during expression experiments. Furthermore pH dependence and signal transduction was analysed.
Reifarth FW, Amasheh S, Clauss W, Weber WM (1997) The Ca2+-inactivated Cl- channel at work: selectivity, blocker kinetics and transport visualisation. J. Membr. Biol. 155: 95-104 [Medline Abstract]
Amasheh S, Weber W (1999) Further characteristics of the Ca2+-inactivated Cl- channel in Xenopus laevis oocytes. J. Membr. Biol. 172: 169-179 [Medline Abstract] [PDF]