Flow Cytometry (FCM) /FACS | Species of Sample

Protein Family

A protein family is a group of evolutionarily-related proteins, and is often nearly synonymous with gene family. The term protein family should not be confused with family as it is used in taxonomy.

Proteins in a family descend from a common ancestor (see homology) and typically have similar three-dimensional structures, functions, and significant sequence similarity. The most important of these is sequence similarity (usually amino acid sequence) since it is the strictest indicator of homology and therefore the clearest indicator of common ancestry. There is a fairly well developed framework for evaluating the significance of similarity between a group of sequences using sequence alignment methods. Proteins that do not share a common ancestor are very unlikely to show statistically significant sequence similarity, making sequence alignment a powerful tool for identifying the members of protein families.

Families are sometimes grouped together into larger clades called superfamilies based on structural and mechanistic similarity, even if there is no identifiable sequence homology.

Currently, over 60,000 protein families have been defined,although ambiguity in the definition of protein family leads different researchers to wildly varying numbers.

Protein Signature

Multiple sequence alignments can provide us with valuable information for protein classification since they allow us to identify the (often few) amino acid residues that are conserved in distantly related proteins. It is not possible to identify such important residues with pairwise alignment techniques, such as BLAST. As a consequence, protein signatures built from multiple sequence alignments are usually better at detecting divergent homologues than pairwise comparison methods. For example, the protein signature built from T-cell surface glycoprotein CD3 gamma chain. Using sequence alignments method, the protein CD3Gs from Human, crab-eating macaque, mouse, rat and bovine have an identity of 50.55%.

Protein Family Tree

The separation of a parent species into two genetically isolated descendent species allows a gene/protein to independently accumulate variations (mutations) in these two lineages evolutionarily. This results in a family of orthologous proteins, usually with conserved sequence motifs. Based on the result, a "tree" was built showing evolution of protein family.

The proteins in same family usually have relatively high sequence homology, structural homology and mechanistic similarity. Therefore, they might be recognized by the same antibody.

Sample from different species list in the antibody datasheet

Even if the proteins of different species with the same name, they may be evolutionarily related, belong to the same protein family, but they may have rather different sequences and tertiary structures. One antibody may most likely not recognize the antigen which is come from different species to the target antigen. To ensure accurate results, you should choose an antibody that has been raised against the same species your sample is from. The antibody may react with the same target protein from other species sharing sufficient amino acid sequence homology.

If your sample is not from one of the species listed in the datasheet, this means that the species has not been tested and we cannot guarantee the performance of the antibody.

Flow Cytometry Antibodies by Immunogen Species