Figure 4. Comparison of SPARC amino acid sequences in the EC-domain essential for Ca²⁺-dependent collagen-binding. Bold letters highlighted in red indicate 5 amino acids found by site-directed mutagenesis to be essential for the Ca²⁺-dependent binding of SPARC to human type I collagen. Note that the essential amino acids are 100% conserved among vertebrates (upper-case underscored letters). Within invertebrates, conservative amino acid substitutions are found at essential sites (upper-case, underscored, and italicized letters). The conservative amino acid changes would be expected to have only minor topographical impact on the collagen-binding domain of SPARC. Fig. adapted from data presented by Sasaki et al.(1998).