Thermobifida alba is the mesophilic member of the Thermobifida
genus, the genome and enzyme sets of which have not been described and published yet.
Thermobifida strains are thermotolerant actinomycete, which
possess wide sets of cellulose and hemicellulose hydrolysing enzymes. Previously,
three endomannanases (Man5ATh, Man5ATc, and Man5AThf) of thermobifidas were cloned
and investigated, and hereby the endomannanase of T. alba
DSM 43795 is described. All four endomannanases belong to the glycoside hydrolase
family 5, their sizes are around 50–55 kDa. Their structure consists of a catalytic
domain and a carbohydrate binding module, while there is an interdomain linker region
in-between consisting repetitive tetrapeptide motifs (eg.: PPTEPTD-Ta, PTDP-Tc, TEEP-Tf,
DPGT-Th). The pH optima of Man5A enzymes from T. alba,
Thermobifida halotolerans, Thermobifida cellulosilytica,
and Thermobifida fusca are slightly different (6.5, 7.0,
7.5, and 8.0, respectively), however, the temperature optima of the enzymes were detected
within a wider range of 65–75 °C. In this research, Man5ATa exhibited the lowest Michaelis-Menten
constant (KM) (0.13 mM) on LBG-mannan substrate, while others shared similar kinetic
parameters: 0.9–1.7 mM of KM. Despite the high sequence similarity of the investigated
mannanases, they exhibit different temperature stability parameters. These different
functional characteristics can be advantageous for industrial applications producing
biologically active, oligomannan prebiotics under different conditions.
