AF007: EF hand family
A wide range of calcium-binding proteins share a conserved domain consisting of a 12 residue calcium-binding loop flanked on both sides by α-helices of 12 residues in length. The biological functions of these proteins can be divided into two classes: signaling and calcium buffering or transport. Signaling proteins such as calmodulin and troponin C undergo a conformational change upon calcium binding .
Allergens from this family
Several groups of allergens were found within this family.
- Polcalcins: Polcalcins are 9 kDa calcium-binding pollen-specific proteins suggested to be involved in pollen germination and pollen tube growth . While regular polcalcins contain two EF hand domains, several polcalcin-related allergens with three or four EF hand domains were described . Polcalcins were shown to be minor albeit highly cross-reactive allergens identified in pollen from diverse plant families .
- Parvalbumins: Parvalbumins are 12 kDa proteins containing two EF hand domains. They are found in fast-twitch muscle fibers of vertebrates and bind Ca2+ during muscle relaxation . Parvalbumins from fishes and amphibians are major food allergens eliciting IgE reponses in most fish-allergic individuals . Parvalbumins from higher vertebrates have not been shown to bind human IgE.
- Troponin C: Troponin is a muscle protein that binds to the thin filaments and initiates muscle contraction upon binding of Ca2+ . Troponin is a complex of three proteins, Ca2+ binding (troponin C), inhibitory (troponin I), and tropomyosin binding (troponin T). Allergens from this family were found in cockroaches and crustaceans (group 6 allergens) [7, 8].
- Sarcoplasmic calcium binding proteins: The invertebrate muscle proteins were proposed to exert a calcium buffering function similar to that of parvalbumins in vertebrate muscle . Members of this family were described as allergens in crustaceans [8, 10].
- Myosin light chain: The myosin molecule is a multi-subunit complex made up of two heavy chains and four calcium-binding light chains. It is a fundamental contractile protein found in all eukaryote cell types. Myosin light chain from invertebrates, such as crustaceans and cockroaches were shown to bind IgE .
The IgE binding capacity of some EF hand-containing allergens was shown to be calcium-dependent.
Structures and metal-ion-binding properties of the Ca2+-binding helix-loop-helix EF-hand motifs.
Biochem J 2007, 405, 199-221. [PubMed] [Full Text]
Expression of Bra r 1 gene in transgenic tobacco and Bra r 1 promoter activity in pollen of various plant species.
Plant Cell Physiol 2000, 41, 757-66. [PubMed]
Molecular and immunological characterization of novel weed pollen pan-allergens.
Allergy 2008, 63, 872-81. [PubMed] [Full Text]
A comparative analysis of the cross-reactivity in the polcalcin family including Syr v 3, a new member from lilac pollen.
Allergy 2006, 61, 477-84. [PubMed] [Full Text]
Calcium ion in skeletal muscle: its crucial role for muscle function, plasticity, and disease.
Physiol Rev 2000, 80, 1215-65. [PubMed]
Fish allergens at a glance: variable allergenicity of parvalbumins, the major fish allergens.
Front Immunol 2014, 5, 179. [PubMed] [Full Text]
Bla g 6: a troponin C allergen from Blattella germanica with IgE binding calcium dependence.
J Allergy Clin Immunol 2006, 117, 1389-95. [PubMed] [Full Text]
Shellfish Allergy: a Comprehensive Review.
Clin Rev Allergy Immunol 2015, 49, 203-16. [PubMed] [Full Text]
Molecular characterization of the sarcoplasmic calcium-binding protein (SCP) from crayfish Procambarus clarkii.
Comp Biochem Physiol B Biochem Mol Biol 2006, 144, 478-87. [PubMed] [Full Text]
Sarcoplasmic calcium-binding protein is an EF-hand-type protein identified as a new shrimp allergen.
J Allergy Clin Immunol 2009, 124, 114-20. [PubMed] [Full Text]
Links to Pfam
Family-defining Pfam domains (at least one of these domains is present in each family member):
Additional Pfam domains found in some family members:
Dynein light chain type 1
Links to Wikipedia
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