ABSTRACT
I. Introduction 59
II. Structure/Function Relationship 62 A. Domains Required for Oligomeric Assembly 62
B. The Globular Domain 64
Carbohydrate Binding and Specificity 66
Lipid Ligands for SP-A and the Nature of SP-A/Lipid Interaction 67
III. SP-A Functions 69
A. Surfactant-Related Functions 69
B. Host-Defense and Immunomodulation of the Inflammatory
Response in the Alveolus 72
Binding of SP-A to Pathogen Surfaces 72
Interaction of SP-A with Immune Cell Membranes 75
IV. Concluding Remarks 77
Acknowledgment 78
References 78
I. Introduction
Surfactant protein A (SP-A) is a large oligomeric apolipoprotein primarily
found in the alveolar fluid of mammalians. SP-A belongs to the “collectin”
(collagen-lectin) family characterized by an N-terminal collagen-like domain
and a globular C-terminal domain that includes a C-type carbohydrate recog-
nition domain (CRD). Collectins bind to a wide range of sugar residues that
are rich in microbial surfaces in a Ca2þ-dependent manner. The collectin family has five well-characterized members: lung surfactant protein A (SP-A)
and D (SP-D), serum mannose binding protein (MBP), serum bovine conglutinin,
and collectin-43 (1). Recently, another novel human collectin from liver (CL-L1)
has been cloned (2). Together with the first component of the complement (C1q),
these proteins are also called defense collagens, and play important roles in innate
immunity (1).
