Lai KK

References (2)

Title : An inserted alpha\/beta subdomain shapes the catalytic pocket of Lactobacillus johnsonii cinnamoyl esterase - Lai_2011_PLoS.One_6_e23269
Author(s) : Lai KK , Stogios PJ , Vu C , Xu X , Cui H , Molloy S , Savchenko A , Yakunin A , Gonzalez CF
Ref : PLoS ONE , 6 :e23269 , 2011
Abstract : BACKGROUND: Microbial enzymes produced in the gastrointestinal tract are primarily responsible for the release and biochemical transformation of absorbable bioactive monophenols. In the present work we described the crystal structure of LJ0536, a serine cinnamoyl esterase produced by the probiotic bacterium Lactobacillus johnsonii N6.2. METHODOLOGY/PRINCIPAL FINDINGS: We crystallized LJ0536 in the apo form and in three substrate-bound complexes. The structure showed a canonical alpha/beta fold characteristic of esterases, and the enzyme is dimeric. Two classical serine esterase motifs (GlyXSerXGly) can be recognized from the amino acid sequence, and the structure revealed that the catalytic triad of the enzyme is formed by Ser(106), His(225), and Asp(197), while the other motif is non-functional. In all substrate-bound complexes, the aromatic acyl group of the ester compound was bound in the deepest part of the catalytic pocket. The binding pocket also contained an unoccupied area that could accommodate larger ligands. The structure revealed a prominent inserted alpha/beta subdomain of 54 amino acids, from which multiple contacts to the aromatic acyl groups of the substrates are made. Inserts of this size are seen in other esterases, but the secondary structure topology of this subdomain of LJ0536 is unique to this enzyme and its closest homolog (Est1E) in the Protein Databank. CONCLUSIONS: The binding mechanism characterized (involving the inserted alpha/beta subdomain) clearly differentiates LJ0536 from enzymes with similar activity of a fungal origin. The structural features herein described together with the activity profile of LJ0536 suggest that this enzyme should be clustered in a new group of bacterial cinnamoyl esterases.
ESTHER : Lai_2011_PLoS.One_6_e23269
PubMedSearch : Lai_2011_PLoS.One_6_e23269
PubMedID: 21876742
Gene_locus related to this paper: lacjo-q74hk5

Title : Biochemical properties of two cinnamoyl esterases purified from a Lactobacillus johnsonii strain isolated from stool samples of diabetes-resistant rats - Lai_2009_Appl.Environ.Microbiol_75_5018
Author(s) : Lai KK , Lorca GL , Gonzalez CF
Ref : Applied Environmental Microbiology , 75 :5018 , 2009
Abstract : Cinnamic acids (i.e., ferulic and caffeic acids) that are esterified to the vegetable cell walls should be enzymatically released to be absorbed in a mammal's intestines. A low dosage of ferulic acid in rodent diets stimulates insulin production and alleviates symptoms caused by diabetes (M. Sri Balasubashini, R. Rukkumani, and V. P. Menon, Acta Diabetol. 40:118-122, 2003). Several lactic acid bacteria are able to display ferulic acid esterase (FAE) activity, suggesting that their probiotic activity could be, in part, mediated by the slow release of ferulic acid. In the present work, we describe the isolation of one strain identified as being Lactobacillus johnsonii that displayed strong FAE activity in stool samples from diabetes-resistant biobreeding rats. These animals are genetically susceptible to becoming diabetic but do not develop the disease. By using genomic analysis coupled to protein purification and catalytic screening, we were able to purify two proteins with FAE activity. The enzymes displayed 42% sequence identity and a broad range of substrate preferences. High affinities and catalytic efficiencies toward aromatic compounds such as ethyl ferulate (K(m) = 20 to 60 microM) and chlorogenic acid (K(m) = 10 to 50 microM) were observed. The strain isolated herein as well as the enzymes studied could be potentially useful for the formulation of probiotics to ameliorate diabetes symptoms.
ESTHER : Lai_2009_Appl.Environ.Microbiol_75_5018
PubMedSearch : Lai_2009_Appl.Environ.Microbiol_75_5018
PubMedID: 19502437
Gene_locus related to this paper: lacjo-q74hk5 , lacjo-q74j82