C-terminal amino acids in the type I transmembrane domain of L-type lectin VIP36 affect γ-secretase susceptibility.

Regulated intramembrane proteolysis (RIP) is a two-step processing mechanism for transmembrane proteins consisting of ectodomain shedding (shedding), which removes the extracellular domain through juxtamembrane processing and intramembrane proteolysis, which processes membrane-anchored shedding products within the transmembrane domain. RIP irreversibly converts one transmembrane protein into multiple soluble proteins that perform various physiological functions. The only requirement for the substrate of γ-secretase, the major enzyme responsible for intramembrane proteolysis of type I transmembrane proteins, is the absence of a large extracellular domain, and it is thought that γ-secretase can process any type I membrane protein as long as it is shed. In the present study, we showed that the shedding susceptible type I membrane protein VIP36 (36 kDa vesicular integral membrane protein) and its homolog, VIPL, have different γ-secretase susceptibilities in their transmembrane domains. Analysis of the substitution mutants suggested that γ-secretase susceptibility is regulated by C-terminal amino acids in the transmembrane domain. We also compared the transmembrane domains of several shedding susceptible membrane proteins and found that each had a different γ-secretase susceptibility. These results suggest that the transmembrane domain is not simply a stretch of hydrophobic amino acids but is an important element that regulates membrane protein function by controlling the lifetime of the membrane-anchored shedding product.

Investigation of 5-(3-Trifluoromethylbenzylidene)thiazolidine-2,4-dione as a Matrix for Analyses of Biogenic Monoamine Transmitters Using MALDI-MS.

In order to discover new matrices suitable for the analyses of low molecular-weight compounds using positive-ion mode matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry (MS), 5-(3-trifluoromethylbenzylidene)thiazolidine-2,4-dione (3-CF3-BTD) was synthesized, and its effectiveness was compared with that when commercially available α-cyano-4-hydroxycinnamic acid was used. 3-CF3-BTD was sufficiently sensitive to analyze neurotransmitters, i.e., dopamine, serotonin, histamine, and epinephrine, in amounts of several picomoles. Similar to vacuum MALDI experiments, atmospheric-pressure MALDI-MS measurements using 3-CF3-BTD as a matrix also detected dopamine.