Fel d 1 is a protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 that in cats is encoded by the CH1 (chain 1/Fel d 1-A) and CH2 (chain 2/Fel d 1-B) genes

Gênes

Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...

.

Fel d 1, produced largely by cat

Cat

The cat , also known as the domestic cat or housecat to distinguish it from other felids and felines, is a small, usually furry, domesticated, carnivorous mammal that is valued by humans for its companionship and for its ability to hunt vermin and household pests...

 saliva

Saliva

Saliva , referred to in various contexts as spit, spittle, drivel, drool, or slobber, is the watery substance produced in the mouths of humans and most other animals. Saliva is a component of oral fluid. In mammals, saliva is produced in and secreted from the three pairs of major salivary glands,...

 and sebaceous gland

Sebaceous gland

The sebaceous glands are microscopic glands in the skin that secrete an oily/waxy matter, called sebum, to lubricate and waterproof the skin and hair of mammals...

s, is the primary allergen

Allergen

An allergen is any substance that can cause an allergy. In technical terms, an allergen is a non-parasitic antigen capable of stimulating a type-I hypersensitivity reaction in atopic individuals....

 present on cats. The protein is of an unknown function to the animal but causes an IgG or IgE

IGE

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 reaction in sensitive humans (either as an allergic or asthmatic response). Removal of soft surfaces in the home (carpet, furniture), frequent washings of bed linens, HEPA

HEPA

High-Efficiency Particulate Air or HEPA is a type of air filter. Filters that are awarded the HEPA accolade are used in various locations, whether in medical facilities, automotive vehicles, airplanes, home filters, or wherever very pure air is sought. The filter must satisfy certain standards of...

 filters and even washing cats have been proven to reduce the amounts of Fel d 1 present in the home. Fel d 1 is a particularly sticky protein and has been shown to cling to clothing and human hair and can be detected in environments where a cat has never been present.

Cats produce, on average, 2-7 µg of Fel d 1 per day. Studies have shown that intact males produce Fel d 1 in levels higher than castrated males, leading to the assumption that Fel d 1 is hormonally regulated by testosterone

Testosterone

Testosterone is a steroid hormone from the androgen group and is found in mammals, reptiles, birds, and other vertebrates. In mammals, testosterone is primarily secreted in the testes of males and the ovaries of females, although small amounts are also secreted by the adrenal glands...

. Neutered males produce Fel d 1 in levels similar to females (both intact and spayed females produce Fel d 1 in similar levels). Even though females and neutered males produce Fel d 1 in lower levels, they still produce enough to cause allergic symptoms in sensitive individuals.

Structure

The complete primary structure

Primary structure

The primary structure of peptides and proteins refers to the linear sequence of its amino acid structural units. The term "primary structure" was first coined by Linderstrøm-Lang in 1951...

 of Fel d 1 has been determined. The allergen is a tetrameric glycoprotein

Glycoprotein

Glycoproteins are proteins that contain oligosaccharide chains covalently attached to polypeptide side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. In proteins that have segments extending...

 consisting of two disulphide-linked heterodimers of [chains 1 and 2. Fel d 1 chains 1 and 2 share structural

Secondary structure

In biochemistry and structural biology, secondary structure is the general three-dimensional form of local segments of biopolymers such as proteins and nucleic acids...

 similarity with uteroglobin, a secretoglobin

Secretoglobin

A family of small disulfide linked dimeric proteins found only in mammals.Family members:...

 superfamily

Superfamily

The term superfamily is used to describe several different concepts in different scientific fields:* Superfamily and Superfamily : a level of biological classification; redirects to Taxonomic rank...

 member; chain 2 is a glycoprotein with N-linked oligosaccharide

Oligosaccharide

An oligosaccharide is a saccharide polymer containing a small number of component sugars, also known as simple sugars...

s. Both chains share an all alpha-helical structure.