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Reference.org
Surfactant protein D
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<p>Surfactant protein D, also known as SP-D, is a <a href="/facts/Pulmonary_surfactant/tAQJxEsI">lung surfactant protein</a> part of the collagenous family of lectins called <a href="/facts/Collectin/zsUrlrGC">collectin</a>. In humans, SP-D is encoded by the <i>SFTPD</i> <a href="/facts/Gene/e1swwPY6">gene</a> and is part of the <a href="/facts/Innate_immune_system/lz4BpSQI">innate immune system</a>. Each SP-D subunit is composed of an N-terminal domain, a <a href="/facts/Collagen/KsyAb72K">collagenous region</a>, a nucleating neck region, and a C-terminal lectin domain. Three of these subunits assemble to form a homotrimer, which further assemble into a tetrameric complex. </p>