第1015回生物科学セミナー
Crystal structure of NRT1.1, the dual affinity nitrate transporter.
Dr. Simon Newstead（Department of Biochemistry University of Oxford）
2014年11月26日(水) 14:00-15:00 理学部3号館 327号室
Nitrogen is an essential rate-limiting nutrient for cellular metabolism in all organisms. The PTR or peptide transporter family, also known as the POT, or proton dependent oligopeptide transporter family, is responsible for nitrogen assimilation in mammals through the uptake of peptides from the environment. In contrast, in the majority of plant species nitrogen is obtained through the uptake of nitrate from the soil. Interestingly the NRT1 family of nitrate transporters phylogenetically belongs to the PTR family, and may have evolved from an ancestral peptide transport protein. In 2003 it was discovered that NRT1.1 has a dual affinity for nitrate. In conditions of high nitrate availability (> 1mM) NRT1.1 behaves as a low-affinity transporter (KM ~4 mM). However, when nitrate levels fall below 1mM,NRT1.1 is switched into a high-affinity transporter (KM 40 μM) following phosphorylation of a specific intracellular threonine. This regulatory mechanism allows plants to respond rapidly between high- and low-affinity nitrate levels, which is critical when competing for limited nitrogen. Recently we determined the crystal structure of NRT1.1. Associated binding studies and in vitro transport assays suggest a complex interplay between substrate affinity and post-translational modification at the molecular level that may have important implications for how phosphorylation may regulate the PTR/POT family of membrane transporters.
