Long-chain and branched polyamines in thermophilic microbes

Abstract

Long-chain and/or branched polyamines such as N 4 - aminopropylspermidine [3(3)4] (abbreviation for the number of methylene CH 2 chain units between NH 2, NH, N, or N +), N 4 -bis(aminopropyl)spermidine [3(3) (3)4], and tetrakis(3-aminopropyl)ammonium [3(3)(3)3] are polycations of biotic origin that are only found in thermophiles. The thermophilic bacterium Thermus thermophilus and the hyperthermophilic archaeon Thermococcus kodakarensis synthesize a polyamine, spermidine, via conversion of arginine to agmatine (a step catalyzed by arginine decarboxylase), aminopropylation of agmatine to N 1 - aminopropylagmatine (catalyzed by aminopropyl transferase), and hydrolysis of N 1 -aminopropylagmatine to spermidine by N 1 -aminopropylagmatine ureohydrolase. It is noteworthy that thermophiles synthesize spermidine without producing putrescine as an intermediate. Spermidine can be modified to produce further polyamides such as N 4 -aminopropylspermidine [3(3)4] and then N 4 -bis(aminopropyl) spermidine by an enzyme coded by the TK1691 gene in T. kodakarensis. TK1691 and its orthologues are found in (hyper)thermophilic Archaea and Bacteria, but not in mesophilic Bacteria. TK1691 is a recently characterized aminopropyl transferase involved in the synthesis of branched polyamines, which are essential for the stabilization and structural protection of nucleic acids and which enhance polypeptide synthesis at high temperature.