Collagens of Poriferan Origin

Abstract

The biosynthesis, structural diversity, and functionality of collagens of sponge origin are still paradigms and causes of scientific controversy. This review has the ambitious goal of providing thorough and comprehensive coverage of poriferan collagens as a multifaceted topic with intriguing hypotheses and numerous challenging open questions. The structural diversity, chemistry, and biochemistry of collagens in sponges are analyzed and discussed here. Special attention is paid to spongins, collagen IV-related proteins, fibrillar collagens from demosponges, and collagens from glass sponge skeletal structures. The review also focuses on prospects and trends in applications of sponge collagens for technology, materials science and biomedicine.

Keywords: biomaterials; collagen; collagen-related proteins; scaffolds; sponges; spongin.

Figure 1

Schematic overview of the collagens and collagen-like structural proteins of poriferan origin described in this review.

Figure 2

The mineral- and cell-free skeleton of commercial Hippospongia communis bath sponge is an example of a 3D spongin scaffold.

Figure 3

Scaning electron microscopy (SEM) image of anastomosed spongin fibers from the demosponge H. communis, which are organized as sets of unconnected structures with dendritic architecture.

Figure 4

Diversity of spongins according to [43].

Figure 5

Sketch of a fragment of spongin framework (b) surrounded by a great number of living cells (a,c) in a sponge-grafting application (adapted from [92]).

Figure 6

SEM view through the collagenous mesohyl of the demosponge S. domuncula. Layers of collagen fibrils (A,B) are a result of the activity of the unique collagen-producing cells which are seen to line up along the surface of the spicules (C–E). The line of cells (A) can move from left to right along the spicule, depositing a rough, nanofibrillar collagenous layer in their wake (C) (see also [114]).

Figure 7

Schematic diagram of C. reniformis collagen fiber with numerous nanofibrils with characteristic nanotopography. Along the fibril, one characteristically thick segment (protrusion) about 28 nm in diameter is followed by two equal thinner and closer conjoined segments (interband) about 20 nm in diameter. The average distance between the protrusions is about 67–69 nm. The distance between two consecutive peaks of the interband regions or between a protrusion and an adjacent interband region is about 21–23 nm. The average step height between the protrusions and the interband regions was calculated to be about 4 nm (see for review [121]).

Figure 8

Photograph demonstrating the unique flexibility of the H. sieboldi anchoring spicule, and schematic view of the role of special hydroxylated collagen in silica condensation in this natural basilica structure (for details see [3]).

Figure 9

SEM image of the nanofibrillar collagenous layer on the surface of an H. sieboldi glass sponge anchoring spicule.

Figure 10

High-resolution transmission electron microscope image of a fragment of M. chuni collagen nanofibril isolated from the glassy spicule (for details see [135]). The nanomorphology of such fibrils is similar to that from H. sieboldi glass sponge collagen [3], but different from the striated collagen fibrils from the demosponge C. reniformis [121].