F-type Lectin Domains: Provenance, Prevalence, Properties, Peculiarities, and Potential 24 Sonal Mahajan and T. N. C. Ramya Abstract F-type lectins are phylogenetically widespread albeit selectively distributed lectins with an L- fucose-binding sequence motif and an F-type lectin fold. Several F-type lectins from fishes have been extensively studied, and structural information is available for F-type lectin domains from fish and bacterial proteins. F-type lectins have been demonstrated to be involved in selfÀ/nonself-recognition and therefore have an important role in pathogen defense in many metazoan animals. F-type lectin domains also have been implicated in functions related to fertilization, protoplast regeneration, and bacterial virulence. We have recently analyzed and reported the taxo- nomic spread, phylogenetic distribution, archi- tectural contexts, and sequence characteristics of prokaryotic and eukaryotic F-type lectin domains. Interestingly, while eukaryotic F-type lectin domains were frequently present as stand-alone domains, bacterial F-type lectin domains were mostly found co-occurring with enzymatic or nonenzymatic domains in diverse domain architectures, suggesting that the F-type lectin domain might be involved in targeting enzyme activities or directing other biological functions to distinct glycosylated niches in bacteria. We and others have probed the fine oligosaccharide-binding specificity of several F-type lectin domains. The currently available wealth of sequence, structural, and biochemical information about F-type lectin domains provides opportunities for the gener- ation of designer lectins with improved bind- ing strength and altered binding specificities. We discuss the prevalence, provenance, properties, peculiarities, and potential of F-type lectin domains for future applications in this review. Keywords F-type lectin domain · L-fucose · Motif · Domain architectures · Structural features 24.1 Introduction to the F-type Lectin Domain The F-type lectin domain (FLD) is a fairly short, ~140 residue domain containing a conserved L- fucose-binding sequence motif, HX(26)RXDX(4) R/K (where X refers to any residue), and a calcium-binding motif, h2DGx (where h refers to a small hydrophobic residue such as Val, Ala, or Ile and x refers to a small hydrophilic residue such as Asn, Asp, or Ser) (Vasta et al. 2008). Several eukaryotic F-type lectins have been well studied biochemically and structurally. Among them is the European eel lectin, Anguilla anguilla S. Mahajan · T. N. C. Ramya (*) Institute of Microbial Technology, Chandigarh, India e-mail: sonalmahajan@imtech.res.in; ramya@imtech.res.in # Springer Nature Singapore Pte Ltd. 2018 K. Chattopadhyay, S. C. Basu (eds.), Biochemical and Biophysical Roles of Cell Surface Molecules, Advances in Experimental Medicine and Biology 1112, https://doi.org/10.1007/978-981-13-3065-0_24 345