Identification of an amphioxus intelectin homolog that preferably agglutinates gram-positive over gram-negative bacteria likely due to different binding capacity to LPS and PGN

Intelectin is a recently described galactofuranose-binding lectin that plays a role in innate immunity in vertebrates. Little is known about intelectin in invertebrates, including amphioxus, the transitional form between vertebrates and invertebrates. We cloned an amphioxus intelectin homolog, AmphilTLN-like, coding 302 amino acids with a conserved fibrinogen-related domain (FReD) in the N-terminus and an Intelectin domain in the C-terminus. In situ hybridization in adult amphioxus showed that AmphilTLN-like transcripts were highly expressed in the digestive tract and the skin. Quantitative real-time PCR revealed that AmphilTLN-like is significantly up-regulated in response to Staphylococcus aureus challenge, but only modestly to Escherichia coli. In addition, recombinant AmphilTLN-like expressed in E. coli agglutinates Gram-negative and Gram-positive bacteria to different degrees in a calcium dependent manner. Recombinant AmphilTLN-like could bind lipopolysaccharide (LPS) and peptidoglycan (PGN), the major cell wall components of Gram-negative and Gram-positive bacteria, respectively, with a higher affinity to PGN. Our work identified and characterized for the first time an amphioxus intelectin homolog, and provided insight into the evolution and function of the intelectin family. (C) 2012 Elsevier Ltd. All rights reserved.